The main distinguishing feature of MAM and MRF technologies is a different polishing substance-instrument:
- a polishing instrument of MAM is a ferroabrasive powder (FAP);
- a polishing instrument of MRF is magnetoreological fluid (MRF fluid)
This distinguishing feature is extremely important and determines all of the main characteristics of MAM and MRF.
MAM technology is effective for preliminary and finishing polishing of the various ferromagnetic and diamagnetic (nonmagnetic) materials: steel and alloys, glass, ceramics, various mono- and polycrystal.
We have some experience of MAM application in place of the thin polishing of metals. We didn't work much on this problem, because out work was accentuated on the finishing technologies of MAM. In the context of VW project it would be possible to study the effectiveness of MAM technology in the place of rough and thin grinding of different materials. The potential of MAM method is huge and is realised at the moment no more than for 20%.
The MRF technology is used only for finishing polishing of the diamagnetic (nonmagnetic) materials: glass, ceramics, nonmagnetic mono- and polycrystal. The potential of MRF method is not that big and is realised at the moment for more than 80%.
The MRF technology is not effective for preliminary polishing (even more so for grinding) because of its low productivity.
The MRF technology can not be used for polishing of ferromagnetic materials, because a high gradient of magnetic induction is created in the contact zone of the polished magnetic surface. This gradient destroys the structure of the magnetoreological fluid and it looses its reological behaviour and efficiency.
Conclusion on item 2 : MAM technology greatly surpasses MRF technology in technological possibilities, potential and score of practical application.
In the process of MAM we mostly use a FAP-composite consisting of "iron-abrasive-polymer (junction)". The abrasive content comes up to 50%. Various materials are used as abrasive: diamond, BN, CeO2, ZrO2, Al2O3, SiO2, etc. Necessary size of abrasive particles is chosen in the range from 20/16 micrometers (for preliminary polishing) up to 10/5 nanometres (for thin polishing). Price and requirements for abrasive and iron powders for FAP are not high. Technology of FAP production is universal for all composition variants and is easy in realisation.
A volume of FAP doze used during MAM is around 2-8 ml (7-30 gr), which is stable at work for 5-30 minutes. There are no special requirement for FAP preparation for work and its storage.
FAP consumption is about 100kg per year. Its price is about 50 USD/kg (34 euros/kg).
The MRFluid is usually used during the MRF process and its content is "iron-abrasive-polymer water solution". The abrasive content is about 5%. High-quality diamond powder or CeO2 are used as abrasive. The size of abrasive particles is 3/0.5 micrometers. Abrasive content more than 5% and abrasive particles bigger than 3 micrometers do not ensure the MRFluid stability. MRF process is not effective with abrasive particles of small size.
During MRF a doze of about 4 litres (16 kg) of MRFluid is used during 12-15 days. Each new doze the consumer has to prepare from the initial components by mixing them during 2 hours. Before each start of MRF the MRFluid should be prepared by thorough mixing during 1 hour.
MRF consumption is about 100 litres (about 400 kg) per year. MRFluid price is 500 USD/kg (340 euros/kg).
Conclusion on item 3: FAP has advantage of MRFluid on all the main characteristics: wide range of application possibilities, simplicity of preparation and usage, economic advantage.
There are 2 schemes of MAM realisation:
- Scheme 1:
- contact of treated surface and polishing environment (FAP) is a localised spot of 1-2 square cm;
- Scheme 2:
- contact of treated surface and polishing environment (FAP) is a ring of 100 and more square cm (this is a scheme for MAM of plate surfaces and surfaces with a big radius of curvature).
MRF process can be realised under a pattern analogical to scheme 1: contact of treated surface and polishing environment (MRFluid) is a localised spot of 1-2 square cm.
Conclusion on item 4: The productivity of MAM process can be 1-2 orders higher that of MRF process.
MAM process can be realised under high values of magnetic induction in the work zone B = 1 Tesla. In strong magnetic fields become strongly apparent plastic magnetic and electric magnetic effects, other physic-chemical processes of energy exchange and mass transfer on atomic-molecular level are activated. These phenomena favour bringing the structure of the processed material to an equilibrium state, "heal" numerous structure defects. As a result it is possible to form a nanorelief of the polished surface with a minimum of structure defects in a pre-surface layer. These phenomena are not studied enough and can be one of the study objects under the project.
MRF process can be realised with the word zone induction of B < 0.3 Tesla. Under B > 0.3 Tesla MRFluid is stratified on composition materials and it looses its operability.
Conclusion on item 5: In contrast to MRF, MAM technology has possibility of the active influence on the formation of nanorelief of polished surface with a minimum structure defects in pre-surface layer. As a result of MAM a significant increase of the most important functional characteristics can be expected – for example: radiation solidity of laser monocrystals; wear, mechanical destruction and corrosion resistance.
MAM installation has 2 main modules:
- module ensuring the process kinematics,
- magnetic system on constant magnets.
MRF installation has 4 main modules:
- module ensuring the process kinematics,
- electro magnetic system,
- module of the constant mixing of MRFluid,
- module of control and ensuring of MRFluid optimal viscosity.
Conclusion on item 6: Equipment for MAM is easier in construction, user-friendly in exploitation and maintenance.
The polishing process productivity is determined by a range of factors (see table below).
|Abrasive content in the polishing environment, % of weight||50||5|
|Maximum size of abrasive particles, micrometers||20||3|
|Maximum induction in the work zone, Tesla||1.0||0.3|
|Contact zone of treated surface and polishing environment, square cm||100 and more||1-2|
Conclusion on item 7: MAM process is many times more productive than MRF process.
MAM technology and MRF technology both ensure the formation of the nanorelief of the surface with roughness height of less than 20 angstroms, which corresponds to a few atomic layers. (For example: lattice constant of silicon a = 5.41 angstroms.)
Both technologies remove a defective layer formed during the previous operation and at the same time carry in almost no proper defects in the formed pre-surface layer.
MAM technology has significant reserves for the increase of the quality of the formed surface layer due to favourable influence of the strong magnetic field on the polishing process (cf. item 5).
Conclusion on item 8: MAM and MRF technologies provide high quality of the formed surfaces. MAM technology has significant reserves of polishing quality increase.
In MAM installations the main energy user is the module providing process kinematics. It uses 1-3 kWt.
In MRF installations the main energy users are the module providing process kinematics and electro-magnetic system. They use about 4 kWt.
Conclusion of item 9: MAM technology has less energy consumption than MRF technology.
MAM technology does not use any ecologically harmful substances and can replace numerous ecologically harmful processes of chemical-mechanical polishing. Recycle of used FAP (around 100 kg per year) does not constitute a complicated problem.
MRF technology does not use any ecologically harmful substances either. Recycle of used MRFluid (around 400 kg per year) does not constitute a complicated problem.
Conclusion on item 10: MAM technology is ecologically harmless. Its application instead of ecologically harmful chemical-mechanical polishing processes with contribute to the preservation of environment.
This table illustrates the main costs of the polishing technology (2008).
|Device cost (approximately), USD (EUR)||50 000|
|Cost of annual polishing environment, USD (EUR)||5 000|
Conclusion on item 11: MAM technology is many times more economical than MRF technology.