JP5020843B2 - Processing method of processing end of electrical steel sheet - Google Patents

Description

  The present invention relates to a technique for improving the fatigue strength and magnetic properties of a processed end portion of an electrical steel sheet used for parts such as automobiles, home appliances, and heavy electric fields, and more particularly, an ultrasonic wave for improving fatigue properties. The present invention relates to a post-processing method using chemical polishing or electrolytic polishing after a hitting process.

  When a repeated load is applied to steel having a machining end face newly generated by a shearing process including punching, the machined portion becomes a notch, and fatigue cracks are generated from the machining end face, leading to fracture. When magnetic steel sheets used in motors for automobiles, home appliances, heavy electric fields, etc. are punched, etc. and used at a high rotational speed, stress concentrates on the processing edge due to the centrifugal force associated with rotation. The problem is fatigue failure. On the other hand, good timing characteristics before machining often deteriorate with machining such as punching, and improvement of fatigue characteristics and magnetic characteristics of the machined part is desired.

  Of these, ultrasonic shock treatment for the purpose of improving fatigue strength of welded parts, etc. has been recently developed for the fatigue fracture problem, and fatigue strength is improved by applying ultrasonic shock treatment to welded parts and machined holes. A method is disclosed in Document 1. The ultrasonic impact treatment refers to the improvement of the surface shape and residual stress caused by plastic deformation by pressing ultrasonic vibrations of several tens of KHz generated from an ultrasonic generator against an object through a tool such as a pin. This is a process of mitigation and reallocation.

  Further, Patent Document 2 discloses a method of applying ultrasonic treatment to the hole edge for the purpose of improving the fatigue strength of the punched portion.

  Furthermore, it is disclosed in Patent Document 3 for the purpose of improving the fatigue strength at the end of the processed part of the electromagnetic steel sheet.

US Pat. No. 6,338,765 JP 2004-115856 JP JP 2007-277650 A

  However, since the ultrasonic impact treatment is a method of applying compressive stress to the surface of the object to be treated with a hard metal, in order to introduce a large amount of compressive residual stress to the treated surface, the surface properties are deteriorated and formed on the surface. The concave portion may become a stress concentration portion and a fatigue crack initiation point, and there is a limit to dramatically improve the fatigue strength. Further, the concave portion formed on the surface has a domain wall pinned, resulting in increased hysteresis loss, which causes deterioration of magnetic characteristics.

  In addition, although compressive stress is introduced into the processed portion, the absolute value is limited due to the shape change, and the ultrasonic hitting method has a limit to dramatically improve the fatigue strength.

  Moreover, the compressive residual stress introduced into the steel surface by ultrasonic peening has a peak at a position within several tens of μm to several hundreds of μm below the surface, and the absolute value of the compressive residual stress is smaller in the surface layer. It became clear that it has the characteristic.

  In view of the current state of the prior art described above, the present invention uses a post-treatment after ultrasonic impact treatment, and is used in automobiles, motorcycle parts, home appliances, etc. In order to improve fatigue and magnetic properties compared to conventional methods in environments where repetitive loads are applied by efficiently introducing large compressive residual stress against the surface and smoothing the irregularities generated at the machining end. It aims at providing the post-processing method after a sonic hit | damage process.

After hitting the processed end of an electromagnetic steel sheet with an ultrasonic vibration terminal, even if the surface of the hit is chemically polished or electrolytically polished, even if the surface is uneven due to ultrasonic hitting, the fatigue strength and magnetic properties are higher than before. there is provided a method for improving fatigue strength and magnetic properties of the processed end portion of the electromagnetic steel sheet capable of securing the characteristics and the gist thereof, the depth 5~15μm from ultrasound striking through the rows have surface -60 to-80 MPa The processed end portion of the electrical steel sheet with the residual stress introduced is etched by 5 to 15 μm by electrolytic polishing or chemical polishing , the fatigue strength of the processed end part of the electrical steel sheet is 200 MPa or more, and the magnetic property is 9 A method for processing a processed end portion of an electrical steel sheet, characterized by strengthening to 5 W / kg (1.5 T / 50 Hz) or less .

  According to the present invention, chemical polishing or electrolytic polishing is performed after the processing method using the ultrasonic impact treatment, so that the residual tensile stress generated at the processing end of the electromagnetic steel sheet is introduced particularly in the direction in which the repeated load acts. The large residual compressive residual stress can be used efficiently and effectively, and the stress concentration is reduced by smoothing the unevenness formed on the surface, and the hysteresis loss due to pinning of the domain wall is further reduced. It is possible to further improve the fatigue characteristics and magnetic characteristics of the processed end portion of the steel plate than before.

  The present invention is described in detail below.

  The present inventor has studied a method for achieving both of the properties of a punched portion of an electrical steel sheet in which improvement of fatigue properties and magnetic properties is a problem.

  First, as a result of examining the deformation state and the residual stress distribution in the vicinity of the end face of the electromagnetic steel sheet punching portion, it was found that the plastic deformation state has the distribution shown in FIG. 1 and the residual stress has the distribution shown in FIG. That is, in the punched portion 4 and the remaining portion 3 that are punched between the die 2 and the punch 1 as shown in FIG. 3, the rear surface side corner portion 6 of the punched portion 4 and the front surface side corner portion 8 of the remaining portion 3 are pulled and deformed. However, compression deformation exists in the front side corner 7 of the punched portion 4 and the back side corner 5 of the remaining portion 3.

  These plastic deformation portions are constrained by the adjacent portions, and as shown in FIG. 2, compressive residual stress is applied to the tensile deformation portions of the back side corner portion 6 of the punched portion 4 and the front side corner portion 8 of the remaining portion 3. Tensile residual stresses are generated in the compression deformed portions of the front surface side corner portion 7 of the portion 4 and the back surface side corner portion 5 of the remaining portion 3. Further, in the adjacent portions 9 to 12 of these deformed portions, the residual stress of the opposite sign that balances the residual stress of the deformed portion, that is, the adjacent portion 9 of the back surface side corner portion 5 of the remaining portion 3 and the surface side corner of the punched portion 4 Compressive residual stress is generated in the adjacent portion 11 of the portion 7, and tensile residual stress is generated in the adjacent portion 10 of the back surface side corner portion 6 of the punched portion 4 and in the adjacent portion 12 of the front surface side corner portion 8 of the remaining portion 3.

  In such a punched portion, in particular, the sharp shape of the back side corner 5 of the remaining portion 3 that comes into contact with the die 2, the unevenness of the processed portion, and the tensile residual generated by compressive deformation centered on the back side corner 5 It was understood that the stress caused the deterioration of fatigue characteristics. In addition, regarding the magnetic characteristics, it was also found that the unevenness of the processed portion was reduced and the generation of compressive residual stress having a certain absolute value improved the magnetic characteristics.

  As a result of diligently investigating the means for solving these problems, the shape of the sharp corners 5 on the back side was improved to improve fatigue strength, while the unevenness of the processed part was improved, and the absolute value of the residual stress of compression was increased to some extent. In order to improve fatigue characteristics and magnetic properties, it is concluded that it is effective to perform ultrasonic impact treatment mainly on the back side corner 5 and / or the front side corner 8 and then perform electropolishing or chemical polishing. It was found to be more effective. Ultrasonic impact treatment transforms ultrasonic energy into vibration energy to give plastic deformation to the object, mainly to improve the surface shape gently following the shape of the tool, and compressive residual stress accompanying plastic deformation The fatigue strength of an object is improved by two effects of generating an effect. The electropolishing method is to improve the fatigue strength and magnetic properties of an object by anodically dissolving a metal surface in an acid or alkaline solution and electrochemically improving the surface smoothly. The chemical polishing method is to improve the fatigue strength and magnetic properties of an object by dissolving the metal surface in an acid or alkali solution and chemically improving the surface smoothly.

  As a result of investigating the stress state of the ultrasonic shock treated portion in detail, as shown in FIG. 1, the back side corner portion 5 undergoes compressive deformation as shown in FIG. 1, resulting in a tensile residual stress. The strain relationship is shown in FIG. The tensile residual stress varies depending on the amount of compressive strain, the volume of the adjacent portion to be balanced, the boundary length, and the like, but is approximately a value corresponding to the yield stress.

  In the present invention, it is desirable to reduce the residual stress by subjecting this portion to ultrasonic impact treatment to give a tensile plastic deformation to have a stress-strain relationship as shown in FIG. Here, even if the tensile strain applied by the ultrasonic impact treatment is slight, the tensile residual stress is reduced, but it is preferable to apply a tensile strain of the same magnitude so as to offset the compressive strain due to the previous punching process.

  The treatment range for improving fatigue strength by ultrasonic impact treatment needs to cover the peripheral plastic deformation region formed with processing and the region covering the region where residual stress is generated. is there. In the present invention, as a result of investigating the composition deformation region and residual stress distribution generated by the punching process, deformation and residual stress are generated due to the influence of processing from the processing end to the range corresponding to the thick plate of the material, It is desirable that the ultrasonic impact treatment is also performed on the steel surface in the range of the plate thickness or more from the processed end.

  The upper limit of the processing length from the processing end is not particularly limited, but when the length of the ultrasonic impact processing is increased, the portion 16 adjacent to the processing portion is balanced with the compressive residual stress of the processing portion 15 as shown in FIG. In order to suppress the increase in the tensile residual stress, the processing length 18 is set to be different from that of the processing unit 15 and other factors. It is preferable that the length between the free end surface 17 is 19 or less.

  As a result of examining the stress state in detail by electrolytic polishing the processed part subjected to the ultrasonic impact treatment, the processed part had a stress distribution as shown in FIG. 6 depending on the amount of electrolytic polishing.

  In the present invention, a processed band is formed by ultrasonic treatment on the surface of the processed portion of the steel sheet, and the processed band is electrolytically polished or chemically polished. Desirably, the processing zone is subjected to electrolytic polishing or chemical polishing at a depth of 1 μm to 20 μm from the surface.

  If compressive stress is present at a place where fatigue occurs, the fatigue life is improved. At this time, the fatigue strength improvement effect is considered to be greater as the surface irregularities are smaller and the absolute value of the surface compressive residual stress is larger.

  Here, with respect to the processing band processing position, when the residual stress on the surface was measured after electrolytic polishing or chemical polishing, the reason why the absolute value of the compressive stress increased was estimated as follows.

  In the ultrasonic hitting method, compressive residual stress is introduced around the processing zone processed by the ultrasonic vibration terminal driven by the ultrasonic wave, but the impact is formed on the surface of the hitting spot (processing zone surface) by the impact. As a result of the change in pressure, a part of the compression residual stress is released. The compressive residual stress is higher in absolute value than the position. However, in a region further inside than the work zone, a tensile residual stress is generated in reverse due to a stress balance.

  From the above results, we assumed the following.

  The value of the compressive residual stress is related to the depth from the impact treatment surface, and the absolute value of the compressive residual stress is increased by making the depth appropriate by chemical polishing or electropolishing from the impact surface. Can do.

  Regarding the processing band processing position, the surface irregularities become smaller after electrolytic polishing or chemical polishing. Here, when the surface irregularities are reduced by polishing, the pinning of the domain wall is reduced, the hysteresis loss is reduced, and the magnetic characteristics can be improved. However, if the absolute value of the compressive residual stress becomes too large to some extent, the eddy current loss increases and the magnetic characteristics deteriorate.

  Based on these ideas, how the residual stress of the processed part changes when the polishing depth is changed using an ultrasonic vibration terminal with a diameter D = 2 mm, and chemical polishing or electrolytic polishing changes. We examined how the unevenness, fatigue properties, and magnetic properties change.

experimental method
UIT device (AppliedUitrasonic): Frequency 27kHz
Diameter of ultrasonic vibration terminal: 2mm,
Output power: Depends on device and device settings
The UIT device can be adjusted from 1 to 9 with the rotating knob attached to the device, but the absolute value is unknown.

(Measurement of residual stress)
The residual stress was measured by X-ray diffraction using the sin2ψ-2θ method. The instrument used for the measurement was MSF-2M manufactured by Rigaku Corporation, the X-ray tube was Cr, the detector was a scintillation measuring instrument, the voltage was 30 kv, the current was 10 mA, and the diffraction line measurement method was tilted. The X-ray incidence method is the ψ constant method, the incident angle ψ is 0 sec, 15 deg, 30 deg, 4 deg. Step, measurement was performed by stepping at a step interval of 0.25 degrees, and the half-width method was used to determine the peak. In the stress measurement, the [211] diffraction surface of ferrite was used, and the physical constants were absorption coefficient 850.04, Young's modulus 21000kgf / mm2, Poisson's ratio 0.28, and stress constant -32.44. The measurement area was 0.5 mm (direction perpendicular to the processing direction) × 6 mm (processing direction).

  FIG. 7 is a diagram showing the relationship of the magnetic characteristics at the processing edge when the processing band of the ultrasonic impact treatment in the present invention is electropolished by the depth d. When the distance electroplated from the surface shown on the horizontal axis in FIG. 7 and the magnetic characteristics are correlated, and the depth is 1 μm or more and 20 μm or less, the magnetic characteristics are more than when the processed part is ultrasonically processed. I understand that is good.

  FIG. 8 shows the relationship between the depth from the surface obtained by chemically polishing or electrolytically polishing the processing zone for ultrasonic impact treatment in the present invention and the fatigue strength of the processed portion (stress range where the fracture life is 2 million times).

  In order to obtain these effects more remarkably, in the processing zone, the surface before the treatment may be hit so as to form an indentation having a depth of several tens of um to a depth of several hundreds of um. desirable.

  A non-oriented electrical steel sheet with a thickness of 0.5 mm is processed into a strip with a width of 108 mm and a length of 500 mm, and the hole shown in FIG. 9 is punched into the central portion of the strip, and ultrasonic shock treatment is applied to the processed portion. gave. The ultrasonic shock treatment apparatus was processed by manually pressing the tool end with a cylindrical pin having a vibration frequency of 26 kHz, a pin amplitude of 25 to 30 μm, and a diameter of 2 mm. The treatment was performed by moving the pin in one direction at a speed of 5 seconds per 1 cm length, and the same part was not treated more than twice.

  A repeated load was applied in the longitudinal direction of the treated test piece, and a fatigue test was performed in a room temperature atmosphere under the conditions of load control and stress ratio R = 0 (complete single swing). Furthermore, the surface roughness Ra was measured for the fatigue crack generation position of the test piece, that is, the portion that hits the circumferential side surface at the end on the back side of the punched portion, and the residual stress was measured by X-ray. The same test piece was evaluated for iron loss according to JEM1432 “Single-plate magnetic test method”. For comparison, a test piece not subjected to ultrasonic impact treatment was also prepared, and similarly, residual stress measurement by X-ray (plus is tensile residual stress, minus is compressive residual stress), fatigue test, and evaluation of magnetic properties were performed. These results are summarized in Table 1.

  No. 1 comparative example without ultrasonic impact treatment, No. 2 comparative example with ultrasonic treatment but no electrolytic polishing or chemical polishing, No. 3 comparative example with ultrasonic treatment but only 0.5 μm electrolytic polishing, Comparative example of No12 with sonication applied but only 0.5μm electropolishing, Comparative example of No10 and No11 with sonication but 30μm and 40μm electrolytic polishing, sonication applied but chemical polishing In the present invention of No4 to No9 and No13 to No18 in which electrolytic polishing or chemical polishing is appropriately performed at 1 μm or more and 20 μm or less after ultrasonic treatment as compared with the comparative examples of No. 19 and No. 20 with 30 μm and 40 μm. Residual stress and Ra at the rear surface side edge (cracking position) are moderately improved, and both fatigue characteristics and magnetic characteristics are improved. Here, in the comparative examples of No. 10 and No. 11 that are subjected to ultrasonic treatment but electrolytic polishing is 30 μm and 40 μm, and in the comparative examples of No. 19 and No. 20 that are subjected to ultrasonic treatment but chemical polishing is 30 μm and 40 μm, Ra at the back side edge (cracking position) is improved, and the residual stress is also increased by the compressive residual stress, so the fatigue strength is improved, but the compressive residual stress is too large, The eddy current loss becomes too large and the magnetic properties are deteriorated.

  As described above, it has been found that the method of the present invention is effective in improving the fatigue characteristics and magnetic characteristics of the processed part of the electrical steel sheet as shown in the examples.

The figure which shows the plastic deformation state of the end surface vicinity of an electromagnetic steel plate punching part. The figure which shows the residual stress distribution of the end surface vicinity of an electromagnetic steel plate stamping process part. The figure which shows the relationship between the stress and distortion of the part (back surface side corner | angular part) by which the ultrasonic impact process was carried out. The figure which shows the process log | history of the die side compression deformation part by processes, such as punching. The figure which shows the process log | history by an ultrasonic impact process. The figure which shows the relationship between the amount of electropolishing of the process part which performed the ultrasonic impact process, and residual stress. The figure which shows the relationship between the amount of electropolishing of the process part which performed the ultrasonic impact process, and a magnetic characteristic. The figure which shows the relationship between the amount of electropolishing of the process part which performed the ultrasonic impact process, and fatigue strength. The figure which shows the process part of the electromagnetic steel plate which performs an ultrasonic impact process.

Claims (1)

Machining end of the electromagnetic steel sheet introduced residual stress of -60 to-80 MPa at a depth 5~15μm from the surface have line ultrasonic striking treatment, in electrolytic polishing or chemical polishing method, 5 [mu] m or more 15 [mu] m or less Etching and strengthening the fatigue strength of the processed end of the electromagnetic steel sheet to 200 MPa or more and the magnetic properties to 9.5 W / kg (1.5 T / 50 Hz) or less, and processing the processed end of the electromagnetic steel sheet .

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