MAM applications
Wide technological possibilities in combination with specially created structures of lubricant-cooling liquids and powders-tools have allowed to realise on practice the processes of the Magnetic-Abrasive Machining (MAM) for the resolution of the following problems:
- Polishing contacting surfaces of details of the machines subject to significant mechanical loading and working on wear, contact and cyclic durability.
- Cleanup surfaces of products before welding.
- Polishing surfaces before and after coatication of coatings.
- Cleanup of products surfaces of oxide films and defective layers.
1. Polishing contacting surfaces in the magnetic field.
An example of MAM application for polishing working paths of rolling bearings rings of a drive of rotation of a helicopter blades is indicative. Polishing these products in the magnetic field has allowed to lower roughness and sinuosity of surfaces in 4-10 times and generate a qualitative superficial layer, which has allowed to improve wear resistance and contact durability on 30-60 % in comparison with a polished surface. Application of MAM is effective for polishing surfaces of a sliding friction, for example, rods of sliders in sewing machines. Wear of the machined by MAM surfaces of rods with diameter of 7 mm was equal to 1-2 mkm during 100 hours of trial tests, and wear of polished rods during the same time was equal to 7-10 mkm. Thus the noise level of rods processed by MAM at work is lower on 30 %. There was developed the MAM technology of screw and smooth cylindrical surfaces of screws, worms, shaft and other details. Polishing in the magnetic field (with simultaneous removal of burrs and curving sharp edges on coils and splines) reduces roughness and sinuosity of surfaces of working coils in 3-6 times, improves quality of a blanket, raises wear resistance and contact durability of coils on 20-40 %. The gear pair of a reducer containing a worm polished in the magnetic field is characterized with the raised loading ability and lowered losses on friction.
2. Magnetic-abrasive cleanup of surfaces before welding.
Qualitative welding of metal products can be executed only after careful cleanup of welded surfaces from oxide films, defects and pollution. Otherwise they get into a body of a welded seam and reduce its durability and corrosion resistance. It is especially inconvenient to prepare for welding a surface of products from chemically active alloys on aluminum, magnesium and titan base. Under the order of space and aviation device-making industry the task of cleanup before welding of elements edges of a design of flying devices-cowlings and plates from Al-Mg alloys was solved. Magnet-abrasive machining on optimum modes from surfaces of edges leave oxide film and pollution. The film which eventually practically on grows is formed thin glass-like oxide and protects the basic metal from corrosion. During welding this film under influence of a flux and a welding arch completely decays and does not bring defects in a formed welded seam. Suitability to welding edges after MAM is not less than 30 days, and for alternative operations like as chemical etching and mechanical scraping this parameter is equal to 0,33 and two days accordingly. Tests of welded seams for mechanical durability (strength, limit of fluidity etc.) have shown, that cleanup of edges in the magnetic field provides higher values of the specified characteristics, than at samples after electrochemical polishing and chemical etching. As IAM does not require application of toxic solutions of acids and alkalis this technology is more preferable both from ecological and economic points of view. Application of MAM proposes good results for cleanup of sheet products surfaces from alloyed (corrosion-resistant) steels before their thermal diffusion welding. As one frequently uses a wire from the same alloy at welding alloys as a fusing electrode, it was required to solve a task of cleanup of a wire surface as well. For these purposes the technology and equipment have been developed, which allow to clean a wire from different alloys on one device.
3. Polishing surfaces before and after coatication of coatings.
In nuclear mechanical engineering the most difficult problem is maintenance of necessary corrosion resistance of external surfaces of envelops of the thermal conducting elements (twels), working in the environment pair at pressure of 200 atm and temperature of 300°C. The envelops are produced from zirconium alloys, and finishing machining is carried out by electrochemical polishing in extremely aggressive solutions of a fluoric acid. This technology is very poor from the environmental point of view and requires high expenses for maintenance of safe working conditions for employees and recycling fulfilled reactants. The undertaken attempt to replace electrochemical processing twels on polishing in the magnetic field has yielded encouraging results. The developed technology and equipment allow to polish external surfaces of twels-pipes and form a blanket with a minimum of structure defects. As a result of magnet-abrasive polishing with usage of passivating additives to a lubricant-cooling liquid a thin glass-like zirconium oxide film was received on a surface of twels-pipes. It is grown up by additional technological methods and gets necessary corrosion resistance in reactor conditions. There was developed an original process of polishing internal surfaces of pipes of rectangular section with sizes from 3x6 mm up to 7x14 mm. Pipes from the copper alloys, used as wave guides of the microwave devices, were polished in the magnetic field, then on the polished surface the silver coating with thickness of about 30 mkm was covered and repeated polishing with condensation of coating and maintenance Ra=0,10-0,05 mkm was carried out. There is experience of magnet-abrasive polishing of chromic and ceramic coatings of different items.
4. Magnetic-abrasive cleanup of surfaces from oxide films and defective layers.
In the magnetic field sheets, belts, bars, wire and other items are cleaned up. Preparation of printed-circuit-boards looks like sheets of glass textolite covered with a copper foil with thickness of 35 mkm. Before coatication of photoresist from a surface of a foil it is necessary to remove an oxide film of copper with thickness of 2-4 mkm and generate a surface with Ra=0,2-0,6 mkm. For operation the machine tool has been developed, which cleans up a foil-clad sheet simultaneously from two sides with productivity of 0,5-4,0 m/min. It makes possible cleanup of sheets and belts from non-magnetic alloys with thickness up to 2 mm and width up to 350 mm on the machine tool. There was worked out a small-sized device for magnet-abrasive cleanup of edges of an enamel-covered wire before connection by soldering, welding or mechanical fastening. Cleanup is made simultaneously by two "brushes" from ferro-abrasive powder generated on periphery of magnetic disks. The edge of a wire is set into a zone of machining on length of cleanup. Paint and varnish coatings and pollution are removed from a surface of a wire during machining, and from an opened surface of the basic metal oxides and a layer of metal with thickness of 2-10 mkm. This is a new formed surface completely prepared for connection by welding or soldering. Diameter of the cleaned up wires is 0,1-3,0 mm, time of cleanup is 3-5 sec.