| WU Jin-zhong,XING Bai-jun,ZOU Yan-hua,ZHENG Fei.Ultra-precision Surface Magnetic Grinding by Low Frequency Alternating Magnetic Field[J],47(11):281-289 |
| Ultra-precision Surface Magnetic Grinding by Low Frequency Alternating Magnetic Field |
| Received:April 27, 2018 Revised:November 20, 2018 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2018.11.040 |
| KeyWord:magnetic abrasive finishing low frequency alternating magnetic field nano processing grinding pressure SUS304 stainless steel plate |
| Author | Institution |
| WU Jin-zhong |
University of Science and Technology Liaoning, Anshan , China |
| XING Bai-jun |
University of Science and Technology Liaoning, Anshan , China |
| ZOU Yan-hua |
University of Science and Technology Liaoning, Anshan , China |
| ZHENG Fei |
University of Science and Technology Liaoning, Anshan , China |
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| Abstract: |
| The work aims to solve the problems of magnetic brush distortion, caking of abrasive particles and lower utilization of abrasive particles by the variable magnetic force from the low frequency alternating magnetic field, so as to obtain ultra-smooth and nanoscale polishing surface. Alternating current with frequency of 3Hz was connected in the electromagnetic coil to generate the low frequency alternating magnetic field. The magnetic flux density of the processing area was measured by the EMIC Gauss Meter GM 4002 to investigate the magnetic field intensity distribution of the low frequency alternating magnetic field. A set of grinding pressure measurement system was designed and assembled and the KYOWA PCD-300A data recording and processing software was used to compare and analyze the magnetic force produced by the low frequency alternating magnetic field and the direct magnetic field. The change law of the grinding tool (magnetic particle cluster) under the action of low frequency alternating magnetic field was deeply studied. A set of plane magnetic grinding machine at low frequency alternating magnetic field was developed. The SUS304 stainless steel plate was used as the processing workpiece, and compared with direct magnetic field to verify the feasibility and processing performance of low frequency alternating magnetic field during the magnetic grinding. The magnetic flux density of each point in the low frequency alternating magnetic field changed continuously between peak value and valley value and, the law of change approximated to the sinusoidal distribution. The maximum value was generated at the pole edge (R=7.5 mm) and the magnetic intensity gradually decreased from the magnetic pole radius (R=6 mm) to the magnetic pole center (R=2 mm). The change law of grinding pressure was periodic change under low frequency alternating magnetic field, and the average value of grinding pressure was larger than that of direct magnetic field. Periodic vibration of magnetic cluster was produced under low frequency alternating magnetic field. When the magnetic cluster was at contraction state, the magnetic particles drove the abrasive particles to the front of the magnetic cluster. When the direction of the magnetic field changed, the magnetic cluster was divergent first, and then contracted. the abrasive particles and magnetic particles were mixed again. This cycle and update not only solved the deformation problem caused by the contact between the magnetic cluster and the workpiece, but also improved the utilization rate of the abrasive particles and ensured the stability of the grinding tool. Low frequency alternating magnetic field and direct magnetic field were used to grind SUS304 stainless steel plate respectively with oily grinding fluid, spindle speed at 350 rad/min, alternating current at 1.9 A (average value) and frequency at 3 Hz. In the first stage, the electrolytic iron powder with an average diameter of 30 μm and the abrasive particles of WA#10000 were selected, and the surface roughness values were improved to 35.28 nm and 81.36 nm after 60 min grinding. In the second stage, the carbonyl iron powder with average particle diameter of 6 μm and diamond powder of 1 μm were selected, the surface roughness reached 4.51 nm and 17.58 nm respectively after 60 min grinding. MAF process by low frequency alternating magnetic field can cycle and update the grinding tool (magnetic cluster) and improve the utilization ratio of the abrasive particles. Compared with the direct magnetic field, the surface obtained by MAF at low frequency alternating magnetic field is uniform and free from scratch, thus realizing the processing of ultra-smooth and nanoscale plane. |
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