JP2563729B2 - Method and apparatus for improving iron loss of grain-oriented electrical steel sheet using pulsed CO2 laser - Google Patents

Description

Detailed Description of the Invention

[0001]

The present invention relates to an products produced by it and the iron loss property improved method and apparatus capable of withstanding the stress relaxation annealing grain-oriented electrical steel sheet significantly the magnetic properties by particular pulsed CO ₂ laser beam irradiation It relates to the processing method to improve.

[0002]

2. Description of the Related Art Conventionally, many means have been proposed as a method for improving the iron loss value of an electromagnetic steel sheet, and among them, the iron loss characteristic is improved by laser beam irradiation disclosed in Japanese Patent Publication No. 57-2252. The method has been widely put to practical use because of its large improvement effect and high reliability and controllability due to non-contact processing. This method is intended to reduce the eddy current loss while suppressing the increase of the hysteresis loss by subdividing the magnetic domain of the grain-oriented electrical steel sheet by the reaction force of the thermal shock wave generated by irradiating the laser beam. Although many methods have been disclosed following the patent publication, all the irradiation conditions of the laser beam are arranged in the dimension of J / cm ² which is the energy density E.

However, the condition of interaction between the laser beam and the substance cannot be defined solely by the energy density E of the laser beam. That is, the energy density E is
In the case of a pulse laser, it is defined by the product of the pulse peak power density P and the pulse half width W, but various combinations of the pulse peak power density P and the pulse half width W are available for the same energy density E. Can exist Further, in the case of a continuous wave laser, the energy density E is defined by the power density P'irradiated for one second, and therefore there may be a plurality of combinations of laser power density and laser beam scanning speed in this case as well. FIG. 4 shows the classification of laser energy according to laser energy and pulse width shown in p. 39 of “Laser Machining” (1976) by Akira Kobayashi, published by Development Co., and even for the same energy as in FIG. It has been shown that by shortening the pulse width, the processing phenomenon changes from the state of only heating the substance to melting and evaporation. Further, it is specified that there is a large difference between the pulsed laser beam and the continuous wave laser beam due to the processing phenomenon. Therefore, defining the condition only by the laser energy density E as a method for improving the iron loss of the electromagnetic steel sheet involves a very uncertain factor.

Next, the condition of interaction between the laser beam and the substance is largely influenced by the absorptance of the laser beam by the substance in addition to the above laser characteristics. The factors that determine the light absorptance are the surface roughness of the steel sheet that is the workpiece, the temperature, the absorption characteristics of the film on the steel sheet surface, and the laser wavelength.
FIG. 5 shows an example of the measurement results of the wavelength dependence of the laser power absorption characteristics on the surface of the electromagnetic steel sheet when the surface roughness and the surface temperature are constant. Lasers generally used industrially are mainly YAG lasers and CO ₂ lasers, and their typical oscillation wavelengths are 1.06 μm and 10.6 μm. Comparing the absorptance of the electromagnetic steel sheet with respect to these two wavelengths, the YAG laser has an absorptance of 35 to 40% at 1.06 μm, while the CO ₂ laser has an absorptance of 10.6 μm.
The absorption rate is 5-10%, which is very low and 1/4 to 1 of the former
Only / 5. Since the laser energy is applied to the steel sheet based on this, the heating, melting, and evaporation phenomena change greatly, and the dependence of the absorptivity on the wavelength of the laser beam cannot be ignored. Kasaruni Shokoku Sho 59-536
In Japanese Patent Publication No. 84 etc., a Q-switchable ruby laser, YAG laser, or C laser oscillator is used.
It is disclosed that any laser such as a continuous wave laser such as an O ₂ laser, an Ar laser or a CO laser can be used.

As described above, in the prior art, the peak power density P of the laser beam, the pulse width W, and the oscillation wavelength λ, which are factors that significantly affect the interaction between the laser beam and the steel sheet, are not specified.

Further, these prior arts are characterized in that a considerably wide range is defined as the irradiation condition and an irradiation trace is left on the surface, but the basis thereof is the crystal grain due to the thermal shock reaction force by the laser beam irradiation. Miniaturization,
Processing until changing the surface shape is not taken into consideration. As a result, there is a problem in that the iron loss improving effect disappears when heat treatment is applied to a magnetic steel sheet whose iron loss has been improved by the conventional technique in a high temperature environment. In Japanese Patent Publication No. 58-50298, the temperature exceeds 600 ° C. It is clearly stated that there is a problem with the heat treatment at. This restriction causes a big problem that the conventional technique cannot be applied to a product material such as a wound iron core that requires a stress relief annealing after laser processing.

Stress relaxation annealing exceeding 800 ° C. (Stress R
eryef Annealing: SRA), the Physica Sc
Ripta., Vol. T24, p36-41, 1988, discloses a method of forming a groove having a depth of 10 to 25 μm at right angles to the rolling direction by using a tooth profile roll. According to this method, 850
It has been experimentally confirmed that the improved iron loss value does not deteriorate even if stress relaxation annealing is performed at 4 ° C. for 4 hours, and this is an epoch-making method that can solve the problems of conventional laser processing. However, there is a problem that the life of the tooth profile roll is short and the production cost is significantly increased because the method is a contact-type processing method and that the electromagnetic steel sheet contains a large amount of Si and thus has a considerably high material hardness. Other methods such as chemical etching and antimony (Sb) doping have been proposed as iron loss improving methods for electrical steel sheets that can realize SRA resistance, but both have limitations in achieving high-speed processing. However, there was a problem that productivity could not be improved.

[0008]

DISCLOSURE OF THE INVENTION The object of the present invention is to resist S
In a method and an apparatus for improving the iron loss characteristics of a grain-oriented electrical steel sheet having RA property, the problems of high cost and low productivity of a conventional process such as tooth profile roll or etching are solved, and high productivity and reliability and An object of the present invention is to provide a method and an apparatus for improving iron loss of grain-oriented electrical steel sheets that can simultaneously realize low cost.

[0009]

SUMMARY OF THE INVENTION The present invention provides a method for forming an indentation substantially perpendicular to the rolling direction of a grain-oriented electrical steel sheet to improve iron loss that can withstand stress relaxation annealing, and an apparatus therefor. Pulse half width is 10n
A pulse Q-switched CO ₂ laser having an initial spike of 1 sec or more and 1 μsec or less and a pulse tail of 100 nsec or more and 10 μsec or less and a light intensity density of a pulse peak portion of 2 × 10 ⁷ W / cm ² or more, The focused laser beam is controlled so that the laser beam has a substantially circular shape with a diameter of 1 mm or less or a substantially elliptical shape with a rolling direction diameter of 1 mm or less and a scanning direction length of 3 mm or less, and a rolling direction width of 0.5 mm. Below, depth 10μ
The present invention provides a method and apparatus for improving iron loss of grain-oriented electrical steel sheet using a pulsed CO ₂ laser, characterized in that recesses of m or more are present at an interval of 2 mm or less in the laser scanning direction and an interval of 10 mm or less in the rolling direction.

[0010]

The present invention will be described in detail below. FIG. 1 shows a structure of a Q-switch CO ₂ laser resonator, which is a main component of the present invention, in a method of improving iron loss of grain-oriented electrical steel sheet having SRA resistance using a pulsed CO ₂ laser according to the present invention, and its configuration. 3 shows a configuration of an optical system for irradiating an electromagnetic steel sheet with an output pulse. The laser discharge part 2 is a part which supplies energy to the laser gas which is a CO ₂ laser medium by discharge excitation in a continuous or pulsed manner, and is shielded from the atmosphere by a total reflection mirror 3 and a total transmission window 4 which constitute a laser resonator. Has been done. A Q-switching device including a confocal telescope 5 and a rotary chopper 6 is installed between the output mirror 7 installed in the atmosphere and the total transmission window 4. The rotary chopper 6 has slits for transmitting the laser beam at regular intervals, and the Q factor, which is the figure of merit of the resonator, increases only when the slits come on the laser optical axis.
Switching is realized. Here, in the case of Q-switching by the rotating chopper of a CO ₂ laser, there is no SRA resistance, but the acousto-optic device which has been a problem in the continuous wave pumped Q-switch YAG laser that has been conventionally used for improving the iron loss of electromagnetic steel sheets. Since there is no upper limit of average output in principle, it is possible to realize high average output, that is, high peak output and high pulse energy at high pulse repetition frequency, and 250k at pulse repetition frequency of 10 kHz or higher.
A peak output of W or more and an average output of 1 kW or more are obtained. This is an average output value of 10 or more typical Q-switch YAG lasers. Further, its pulse peak output is a value more than 250 times that of a normal pulse pumped YAG laser. Table 1 shows the results of comparison of typical oscillation characteristics of these various pulse lasers.

[0011]

[Table 1]

The pulsed laser beam 1 extracted from the Q-switch CO ₂ laser resonator is scanned in the plate width direction of the electromagnetic steel plate 10 by the rotary scanner by the polygon mirror 8 and reflected by the plane total reflection mirror 11 to form a parabolic surface. After being focused by the mirror 9, the electromagnetic steel sheet 10 is irradiated.

FIG. 2 shows a pulse repetition frequency of 12 kHz.
₂ shows a Q-switch CO ₂ laser pulse waveform in the case of Q-switch oscillation in FIG. The initial spike part is a giant pulse oscillation part peculiar to the Q switch laser,
The full width at half maximum varies depending on the discharge excitation intensity, the laser cavity length, and the pulse repetition frequency, but the range is 10n.
It is not less than sec and not more than 1 μsec. Furthermore, the Q-switched CO ₂ laser pulse has a long tail after the initial spike. This is a part of the laser pulse oscillated due to energy transfer due to collision of CO ₂ molecules from the N ₂ excited molecule contained in the laser medium with the laser upper level. The maximum length of this tail part is determined by the time constant of collision energy transfer and is about 10 μsec.
Is. This is a pulse tail peculiar to the Q-switch CO ₂ laser which is not found in the Q-switch YAG laser. In Q switching using the rotary chopper, the pulse tail length can be shortened by appropriately changing the width of the laser light transmitting slit.

The maximum value of the pulse repetition frequency during Q-switch oscillation is the delay time until the Q-switch pulse oscillation occurs after the resonator Q value rises, and the energy to the laser upper level while the resonator Q value is low. Is determined by the balance of the storage time, but when the Q-switch oscillation is performed using a general continuous wave CO ₂ laser, a frequency up to about 100 kHz can be realized. When the frequency is lowered below this, 20 k corresponding to the life of the upper level of the laser (about 50 μsec depending on the laser gas composition and pressure)
In the region up to the pulse repetition frequency of about Hz, the pulse energy and the pulse repetition frequency have an approximately inversely proportional relationship, that is, a constant laser average output is obtained.

The Q switch pulse CO as shown above
_{2 The} iron loss characteristic improvement when the grain oriented electrical steel sheet is irradiated with _two lasers will be described in detail below. First, regarding the effect of the pulse peak power density of the initial spike portion on the iron loss characteristics, the characteristics were investigated by sequentially changing the pulse peak output with the laser condensing diameter being a constant value of about 500 μm. As a result, the pulse half width of the initial spike portion is 10n
In the case of a Q-switched CO ₂ laser pulse of sec to 1 μsec, if the peak power density is in the region of 2 × 10 ⁷ W / cm ² or more, a recess having a depth of 10 μm or more is formed, and even if stress relaxation annealing is performed, the It was found that the iron loss improving characteristics did not disappear. Specifically, when a laser pulse with a peak output of 150 kW is focused on a diameter of 1 mm (peak power density 2 × 10 ⁷ W / cm ² ), the depth of the recess is 10 μm, and the same pulse has a diameter of 0.6 mm. When condensed (peak power density 5 × 10 ⁷ W / cm ² ), the depth of the recess was 30 μm. The peak power density is 2 × 10
^When it is less than ⁷ W / cm ² , it is found that the SRA resistance cannot be obtained because the depth is insufficient, although there are some conditions under which the recess is formed. Further, even if the peak power density is extremely increased, the power is absorbed by the plasma generated by the laser beam irradiation, so that the hole machining depth is saturated even if the power density is increased, so there is no particular upper limit. Therefore, the drilling depth is limited to a region of 10 μm or more, and the peak power density is limited to a region of 2 × 10 ⁷ W / cm ² or more.

Next, the laser peak power density can be controlled by changing the laser focusing shape while keeping the peak output constant, so that the laser output is kept constant and the focal length of the focusing lens is changed sequentially. The processing characteristics by laser beam irradiation were evaluated. As a result, if the diameter of the laser beam in the rolling direction of the steel sheet exceeds 1 mm, the machined hole diameter becomes 0.5.
It has been found that the diameter of the laser beam is more than 1 mm, the magnetic domain refining effect after stress relaxation annealing is significantly deteriorated, and the laser beam diameter needs to be 1 mm or less. It is considered that this is because if the strained region formed by laser processing becomes too wide, the magnetic domain subdivision becomes difficult to occur. In addition, here, the lower limit is not particularly specified for both the laser beam converging diameter and the rolling direction hole diameter, but it is impossible to make the converging diameter of the laser beam infinitely small. This is because the lower limit value is naturally defined by the diffraction limit when the focal length and the like are given. From the above results, the laser beam diameter is 1 mm
The peak power density is 2 × 10 ⁷ W /
Since the value is cm ² or more, the value required for the peak value of the laser pulse is 150 kW or more. It was also found that the beam diameter in the laser beam scanning direction was not as strict as the beam diameter in the rolling direction. here,
The pulse peak output is approximately proportional to the pulse energy, and the pulse energy is inversely proportional to the pulse repetition frequency as described above. It is equivalent to take out a high peak output at a repetition frequency and focus it in a linear shape (elliptical shape). Such scanning of the linear focusing in the width direction of the steel plate is realized by inserting a cylindrical mirror or a cylindrical lens into the laser beam focusing system as shown in FIG. In the figure, the laser beam 1 ', which is incident on the polygon mirror 8 from a certain direction, is the polygon mirror 8
Is rotated to scan from the left side 9 _L to the right side 9 _R of the parabolic mirror 9 and is linearly condensed by the cylindrical lens 12. The laser beam condensing diameter d _y in the y direction in the figure is determined by the parabolic mirror 9
And the condensing diameter d _{x in the} x direction are determined by the compound focal length of the cylindrical lens 12, and the converging characteristic of the parabolic mirror 9. The length in the laser scanning direction in the case of linear focusing is determined by the peak output that can be taken out from the oscillator and the peak power density required from the processing conditions, and its upper limit value is 3 mm.

Next, the effect of the pulse tail portion peculiar to the Q switch CO ₂ laser pulse on the laser processing characteristics will be described. The length of the pulse tail portion can be controlled by changing the slit width of the rotary chopper as described above. Therefore, the effect on the processing characteristics was investigated by changing the length of the pulse tail portion sequentially. As a result, high quality drilling can be realized even if there is no pulse tail part.
Further, it was found that the addition of a pulse tail of 100 nsec or more improves the adhesion of foreign matter to the periphery of the hole-processed portion, further improving the processing quality. Adhesion of swelling or foreign matter around the processed portions of the steel sheet surface after the need to prevent as much as possible in order to significantly degrade the transformer efficiency upon the electromagnetic steel plates in the stacked state, which the Q-switch CO ₂ laser according to the present invention It is one of the best features to use. It is considered that the effect of the pulse tail is that the spatter and the like generated by the irradiation of the initial spike portion are heated and evaporated by the reheating effect of the steel sheet by the tail portion.

As described above, it was found that the effect of the domain refinement due to the strain introduced by the hole processing by laser beam irradiation requires the formation of recesses having a width of 0.5 mm or less and a depth of 10 μm or more in the rolling direction. Further, as a result of evaluation by appropriately changing the irradiation interval on the surface of the steel sheet, the interval is 2 mm or less in the laser beam scanning direction under both conditions of point-shaped condensing and linear condensing. is necessary. If this spacing becomes too wide, the effect of the portion where no strain is introduced becomes large and the iron loss improving effect becomes unclear. As to the lower limit of the gap in this direction, there is no particular lower limit, as can be seen from the fact that the conventional tooth profile roll is used for continuous grooving. Similarly, with respect to the rolling direction as well, as a result of experimental evaluation, in order to maintain the effect of introducing strain, the interval must be 10 mm or less, and the lower limit value is naturally determined from the viewpoint of productivity by laser processing. However, it has been found that there is no particular limit in product quality regarding magnetic properties.

In the above description of the present invention, Q
The switched CO ₂ laser has been shown with an example in which a continuous wave oscillating laser by continuous wave discharge is operated in Q switch, but when it is necessary to obtain a large pulse peak output, the inventors of the present application filed a patent application 3 A Q-switched CO ₂ laser in which the pulsed discharge excitation and the rotary chopper Q-switch presented in US Pat. No. 4,252,96 are synchronized may be used. Further, as a Q switching method, a method using a rotary chopper is presented, but it is also possible to use a pulse Q switch CO ₂ laser to which another Q switch method using a rotating mirror, Fabry-Perot etalon, electro-optical element, etc. is applied. Is. Furthermore, in the above description, the wavelength tunability, which is another major feature of the CO ₂ laser, was not particularly explained, but the wavelength dependence of the light absorption rate of the insulating film that is usually applied to grain-oriented electrical steel sheets is not explained. It is also possible to irradiate with the laser oscillation wavelength tuned together.

[0020]

EXAMPLE An iron loss improving method for grain-oriented electrical steel sheet using a pulsed CO ₂ laser according to the present invention was carried out by using the constitution shown in FIG. The laser discharge part 2 is a discharge excitation part of a continuous wave oscillation CO ₂ laser, and has an ability to obtain a laser output of 3 kW in a TEM ₀₀ mode when continuous wave oscillation is performed in a free running mode. The total reflection mirror 3 has a wavelength of 10.
It is a ZnSe reflecting mirror that has been subjected to multilayer film vapor deposition having a reflectance of 99.8% at 59 μm. Total transmission window 4 has wavelength 1
Z with 0.59μm anti-reflection coating
It is an nSe window. The confocal telescope 5 is composed of two ZnSe lenses having a focal length of 100 mm and having the same coating. Rotating chopper 6 is 60,000
A metal blade rotating at 0 rpm, and 10 to 100 slits are introduced on the chopper blade. Therefore, the pulse repetition frequency is 10 to 100 kHz
Is. The average output when the laser is oscillated in the free running mode under the above conditions is about 1200 W or more. The laser beam 1 extracted from the laser resonator is scanned by the polygon mirror 8 in the width direction of the steel sheet over 350 mm. In the case of point focusing, the laser beam 1 is focused on the surface of the steel plate 10 into a beam having a diameter of 0.5 mm by the parabolic mirror 9, and in the case of line focusing, by introducing a cylindrical lens 12 (not shown). About 0.4 mm x 3 mm
Is focused into a linear beam of.

[Embodiment 1] Pulse repetition frequency 50 k
The laser beam of Hz and wavelength of 10.59 μm is focused on a point
A Q-switch CO ₂ laser pulse with a pulse half width of 250 nsec and a pulse tail of ₂ μsec in the initial spike portion
The peak power density of the initial spike part is 5 × 10 ⁷ W / c
As m ² , irradiation was performed at 0.5 mm intervals in the laser beam scanning direction and at 6.5 mm intervals in the steel plate rolling direction. As a result, a total iron loss improvement rate of 9% was obtained for the unirradiated material, and this value did not change even when stress relaxation annealing was performed. This improvement rate is the same value as the improvement rate by the tooth profile roll.

[Embodiment 2] Pulse repetition frequency 10 k
Line-focus a laser beam with a frequency of Hz and a wavelength of 10.59 μm,
The peak power density of the initial spike portion was 3 × 10 ⁷ W with a Q-switched CO ₂ laser pulse having a pulse half-width of 200 nsec and a pulse tail of 2.5 μsec.
/ Cm ² was irradiated at 0.5 mm intervals in the laser beam scanning direction and at 6.5 mm intervals in the steel plate rolling direction. As a result, the iron loss improving effect equivalent to that of Example 1 was obtained.

[0023]

As described above, according to the iron loss improving method for grain-oriented electrical steel sheet using the pulsed CO ₂ laser according to the present invention, since it has SRA resistance, it cannot be applied to the conventional products by laser irradiation. It can also be applied to materials for wound iron cores, and its applications can be greatly expanded. Furthermore, as compared with the conventional method using a tooth profile roll, which is an iron loss improving method with SRA resistance, since it is non-contact processing, there is essentially no wear of the members associated with the processing, so at low cost. It has a great advantage that a process with high reliability and high productivity can be realized.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing the configuration of an embodiment of an iron loss improving method for a grain-oriented electrical steel sheet using a pulsed CO ₂ laser of the present invention.

FIG. 2 is a typical measurement result example of an oscillation waveform of a Q-switch CO ₂ laser.

FIG. 3 is a schematic diagram showing a configuration of a linear beam focusing optical system.

FIG. 4 is a schematic diagram showing classification of laser processing according to laser energy and pulse width.

FIG. 5 is a diagram showing measurement results of wavelength dependence of laser absorption characteristics on the surface of an electromagnetic steel sheet.

[Explanation of symbols]

 1: Pulsed laser beam 1 ': Laser beam applied to polygon mirror 2: Laser discharge part 3: Total reflection mirror 4: ZnSe total transmission window 5: Confocal telescope 6: Rotating chopper 7: Output mirror 8: Polygon mirror 9: Parabolic mirror 10: Electromagnetic steel plate 11: Planar total reflection mirror 12: Cylindrical lens

Claims (3)

(57) [Claims] 1. A method of forming a recess substantially perpendicular to the rolling direction of a grain-oriented electrical steel sheet to improve iron loss capable of withstanding stress relaxation annealing, wherein a laser oscillator has a pulse half width of 10 nsec or more and 1 μsec or less. Using a pulsed Q-switched CO ₂ laser with a width, the light intensity density at the pulse peak is 2 × 10 ⁷ W / cm ² or more, and the focused laser beam is approximately circular with a diameter of 1 mm or less or the rolling direction diameter is 1 mm. In the following, the laser beam is radiated by controlling the laser beam so that the scanning direction becomes a substantially elliptical shape with a length of 3 mm or less
Rolling direction width 0.5 mm or less, depth 10 μm or more recesses in laser scanning direction interval 2 mm or less, rolling direction interval 10 mm
A method for improving iron loss of grain-oriented electrical steel sheet using a pulsed CO ₂ laser, which is characterized in that: 2. The Q-switched CO ₂ laser pulse according to claim 1 has a pulse half width of 10 nsec or more and 1 μsec.
The iron loss improving method for a grain-oriented electrical steel sheet using a pulsed CO ₂ laser according to claim 1, further comprising a pulse tail having the following initial spike and 100 nsec or more and 10 μsec or less. 3. CO in which the laser output window is replaced with a total transmission mirror
_Two lasers, one set of telescope optical system that satisfies the confocal condition, a partial transmission mirror that constitutes the resonance total reflection mirror and the resonance system of the CO ₂ laser, and a laser beam that is transmitted at the confocal position of the telescope. A Q-switch CO that oscillates a laser pulse having an initial spike with a half-value width of 10 nsec or more and 1 μsec or less and an initial spike peak output of 150 kW or more in combination with a chopper that cuts off.
₂ laser, a scanner that scans the laser beam almost at right angles to the rolling direction of the steel sheet, and a laser beam with a light intensity density of 2 × 10 ⁷ W / cm ² or more at the pulse peak portion of the laser beam on the steel sheet surface. It is composed of a lens or mirror that condenses the beam so that it has a substantially circular shape with a diameter of 1 mm or less or a diameter in the rolling direction of 1 mm or less and a length in the scanning direction of 3 mm or less, and has a width of 0.5 mm in the rolling direction on an electromagnetic steel plate. A grain-oriented electrical steel sheet using a pulsed CO ₂ laser is characterized in that recesses having a depth of 10 μm or more are formed with a laser scanning direction spacing of 2 mm or less and a rolling direction spacing of 10 mm or less to improve the iron loss value of the electrical steel sheet. Iron loss improvement device.