Key Engineering Materials 373-374 (2008) pp 824-827 online at http://www.scientific.net © (2008) Trans Tech Publications, Switzerland Online available since 2008/Mar/07 Study on the Polishing Characteristics of the Magnetic Abrasives Finishing to the Slender Pipe Y. Chen 1.a, F.Yan 1.b and C.Q. Zhu1 1Department of Mechanical Engineering, University of Science and Technology Liaoning, 114051, China [email protected], [email protected] Keywords: Magnetic abrasive finishing, Magnetic flux, Magnetic abrasive particles and Slender pipe Abstract. Polishing the inner surface of slender pipe is very difficult. Because a usual tool cannot into the inner surface of the slender pipe, and automation do not achieved easily; the eye is unable to see, even if handmade is also very difficult. Utilize the characteristic of the magnetic force line may penetrate the non-magnetic material, may using the magnetic abrasive finishing (MAF) method complete to the inner surface of the slender pipe precise polishing is a preferable method and already obtained the good processing effect through the experiment. Therefore, this paper analysis and explanation the finishing principle and experiment device as well as collocation position of magnetic poles etc best experimental condition. Introduction Recent years, high precision pipe appeared in medical instrument, astronautics industry and so on. Because transporting mediums is the high-purity gas or the liquid, the lower roughness is requested in internal surface for guaranteed the transportation unobstructed, avoids the pollution and the corrosion, and enhances the duct service lifetime. Because of the placed environment limit, very many ducts are slender pipe, use the ordinary tool is very difficult to machining, even by the handwork is difficult to complete too. The magnetic abrasive finishing may is a preferable solves method to polishing inner surface of slender pipe for the fact mentioned above. The magnetic abrasive finishing is a method that the magnetic field (magnetic force lines) is used to precise polishing the surface of the workpiece. When All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, www.ttp.net. (ID: 221.203.55.194-08/07/08,03:02:11) Key Engineering Materials 373-374 825 the workpiece is inserted between N-S magnetic poles, and the magnetic abrasive particles are filled into the inner of the workpiece, because of effect of the magnetism, the magnetic abrasive particles become a hard magnetic brush along the magnetic force lines (magnetization is generated). When the relative movement between the workpiece and magnetic poles is given, the magnetic brush will press and polish the inner surface of the workpiece (fig. 1 show). The shape of magnetic brush be changed along with the workpiece shape change, not accepting surface shape of the workpiece restricting, have very good flexibility. Another, because the magnetic force lines penetrate nonmagnetic workpiece just like X-ray penetrate objects, therefore, magnetic abrasive particles may to enter the arbitrary shape inner surface which the ordinary cutting tool is unable to enter. Through changes exterior magnet pole position change the direction of magnetic force line for control the magnetic abrasive particles according to the stipulation track polishing inner surface of the workpiece. Polish device of nonmagnetic material workpiece When the workpiece is nonmagnetic material, the workpiece cannot be magnetizing in the magnetic field. Figure 2(a) show, form a magnetic field by the two magnetic poles on the side of the workpiece, put the strong magnetic abrasive particles (abrasive particles on the surface of the magnetic particles) into the inner of the slender pipe that placed in this magnetic field. Utilize the characteristic of magnetic force line can pierce the nonmagnetic material, the magnetic abrasive particles accepts effects of the centrifugal force, magnetic force and the friction, that show itself turn, separate, recombine and distortion phenomenon, stimulated the magnetic abrasive particles cutting edge metabolism, thus precision polishing to the inner surface of the nonmagnetic pipe. Even if the surface of the workpiece appears concave-convex or free curved surface, these surfaces been polished too. Toward biggish caliber workpiece, because the spacing is bigger between the two magnetic poles, the magnetic field intensity being reduces; magnetic force be accepted by magnetism abrasive particles are less, polishing efficiency no highly. For this problem, figure 2(b) show, may add a pair of magnetic pole in the inside of the pipe. The internal magnetic pole and the external magnetic pole mate forming the new magnetic field, not only decrease magnetic pole spacing, have changed direction of magnetic lines and enhancing the magnetic force. On the other hand, cutting notch in the 826 Surface Engineering magnetic pole, can the restraint magnetism abrasive particles disperse to the outside, concentrates polishing force and improves grinding efficiency too. Polish device of magnetic material workpiece When workpiece is magnetic materials, workpiece is become new magnetism pole in the magnetic field by magnetization. External magnetic force lines are shielded by outside surface of the workpiece, magnetic force unable enters to inside of workpiece(fig. 3a show). Therefore, magnetic abrasive particles cannot accept magnetic force in the inner of the pipe, also cannot accomplish polishing processing to the inner surface of the workpiece. Therefore, setting internal magnetic pole mode is a necessary method(fig. 3b show). The magnetic abrasive finishing need about 2-3 mm space between the magnetic pole and the workpiece for magnetic abrasive particles rolls in the inner of the workpiece. If the workpiece aperture is a small size, example is 8 mm, well then, the magnetic pole diameter must is only 3 mm. When inserted the magnetic pole in the inner of workpiece, if only has an eccentricity slightly, the magnetic pole be attached to one side of the magnetized workpiece, which is unable to polishing processing. Therefore, with regard to small diameter slender pipe of the magnetic materials workpiece, magnetic abrasive finishing always a forbidden area, become the problem being difficult to solve. Key Engineering Materials 373-374 827 To this problem, lays a stainless steel axis, which being smaller diameter than the workpiece in the inner of the workpiece and fixes the both ends, slotting and inserting permanent magnet in the centre of the stainless steel axis. Figure 4 shows, because the inner walls of the workpiece is magnetized become a new magnetic pole, that workpiece rotates and the magnetic pole displacement (along the axes direction), as a result of the centrifugal force and the magnetic force as well as the friction effect, magnetic abrasive particles polishing the inner surface of the workpiece. Processing result be showed by figure 5. Summary The magnetic abrasive finishing is a new processing technology, because the finishing tool is tiny magnetic abrasive particles, have good flexibility, do not accept restricting of the workpiece form, can into the workpiece’s arbitrarily location and control easy etc merit. 1. When polishing the inner surface of the nonmagnetic materials workpiece, even if be complicated form, the magnetic pole may place at the outside of the workpiece, throws the magnetic abrasive particles into inner of the workpiece. Because of the magnetic force function, the magnetic abrasive particles attached to the inner surface of the workpiece; when workpiece rotates, the magnetic abrasive particles precision finishing and eliminate the burr thoroughly to the inner surface of the workpiece. 2. When polishing the inner surface of the magnetic materials workpiece, the magnetic pole places at workpiece inside, form a closed magnetic lines circuit between magnetic pole and magnetized workpiece. When workpiece rotates and the magnetic pole makes the axial translation, magnetic abrasive particles precision finishing and eliminate the burr thoroughly to workpiece’s inner surface. 3. Finish to the inner surface of the slender pipe is a difficult problem. Utilize magnetic abrasive finishing method can make such similar problem get solving. 4. When workpiece is thin-wall or bad rigidity, that is easy deformation in the strong magnetic field, which affects the processing quality. Therefore, must prudent choose the experimental condition and reasonableness design the device. Acknowledgement The work described in this paper was supported by Anshan science and technology research fund. (Subject number: 2007SF13) References [1] Y. Chen: J. Iron Steel Res Vol. 6 (2002), p. 24 [2] T.Shinmura and H. Yamaguchi: J. Jpn. Soc. Abrasive Technol Vol. 4 (2000), p. 36 [3] Y. Chen and Y.D. Gong: J. Mater Technol Vol. 20 (2004), p. 117 [4] Y. Chen and D. Y. Ju: CAID & CD, Holand, 2005, p. 47 [5] Y. Chen: Mould Manufacture Vol. 7 (2004), p. 61 [6] Y. Chen and D. Y. Ju: Machinery, Vol. 4 (2005), p. 56 [7] Y. Wang and D.J. Hu: Machine Tools & Manufacture, Vol. 745(2005), p. 43