The document discusses magneto rheological finishing (MRF), a fine finishing process that uses magneto rheological fluid to remove material from brittle materials. MRF was developed in 1988 and commercialized in 1996. It relies on carbonyl iron particles and abrasives in a carrier fluid that form chains when exposed to a magnetic field, allowing for controlled removal of material. The document outlines the components of MR fluid, parameters that affect the polishing forces and material removal rate, advantages, and applications for finishing optical lenses and other precision surfaces to nanometer levels of smoothness without damage.

2.  Introduction
 History
 MR Fluid
 Equipment
 Force analysis in MRF
 Material removal
 Process parameters
 Process capabilities
 Advantages
 Applications
 Conclusion
 References

3.  Magneto rheological finishing is a fine finishing
process that has been applied to a large variety of
brittle materials, ranging from optical glasses to hard
crystals.
 Under the influence of a magnetic field, the carbonyl
iron particles (CIPs) and non-magnetic polishing
abrasive particles remove material from the surface
being polished.

4.  1988- MRF process developed by a team led by William
Kordonski at Luikov Institute of Heat and Mass Transfer in
Minsk, Belarus.
 1993- Concept of using MRF as automated process to polish
high precision optics introduced by Center of Optics
Manufacturing at the University of Rochester.
 1996- MRF technology commercialized by QED Technology.

5.  Magneto rheological finishing process relies for its performance
on magneto rheological effect exhibited by carbonyl iron
particles along with abrasive particles in non-magnetic carrier
medium.
 So, magneto rheological fluid and its composition are crucial in
MRF processes.
 There are basically four components in an MR fluid :-
 A. Base fluid,
 B. Metal particles
 C. Abrasive particles
 D. Stabilizing additives.

6.  BASE FLUID:-
 The base fluid is an inert or non magnetic carrier fluid in
which the metal particles are suspended.
 Water , hydrocarbon oils, mineral oils and Silicon oils ,
glycols
 METAL PARTICLES:-
 Carbonyl iron, Powder iron and Iron Cobalt alloy powder
 ABRASIVE PARTICLES:-
 Silicone carbide, Aluminium oxide, Cerium oxide, Boron
carbide
 STABILIZING ADITIVES:-
 Glycerol, Grease, Oleic acid, Xanthanum gum, Ferrous
oleate , Lithium stearate

7. Chain formation in magnetorheological polishing fluid,
a) Abrasives & Carbonyl iron particles at zero
magnetic fields;
b) Abrasive particles embedded in CIP chains on
application of external magnetic field.

8.  Optimum concentration of magnetic particles and
abrasive particles
 High yield stress under magnetic field
 Low off-state viscosity
 Less agglomeration and good redispersibility
 Temperature-stable
 Resistance to corrosion
 Stability against static sedimentation
 High polishing efficiency
 The viscosity of base fluid should be temperature
stable in a predefined range

10.  Two type of forces act on an abrasive particle
 1. Normal Force(Fn)- penetration of abrasive inside the
work piece.
 Due to magnetic levitation force by magnetic particles and
squeeze during flow in converging gap.
 Presses abrasive against work piece.
 2. Tangential Force(Ft)- removal of material in form of
micro/nano chips.
 By the shear flow of MR fluid.
 Pushes abrasive forward.
 The resultant force (Fr) removes material from work piece.

11. (a) Forces acting on abrasive particle , (b) Force diagram in MRF process

12. •A convex lens is installed at a fixed distance from a
moving wall, so that the lens surface and wall form
a converging gap.
•An electromagnet is placed below the moving wall,
generates magnetic field in the area of gap.
•The MR fluid is delivered to the moving wall just
above the electromagnet pole pieces to form a
polishing ribbon.

13. Material removal mechanism in Magneto rheological Finishing

14. •The ribbon moves in the magnetic field, it acquires
plastic Bingham’s property.
•Then the ribbon pulled against the moving wall by
magnetic field gradient and is dragged through the
gap resulting in material removal over lens contact
zone.
•The area designated by polishing spot.

16.  Concentration of CIPs
 Working gap
 Abrasives Concentration
 Wheel rotation

17. Effect of carbonyl iron particle(CIPs)concentration(abrasive=5%,
working gap=1 mm, wheelspeed=300 rpm)and working
gap(CIPs=40%, abrasive=5%, wheel speed=300 rpm)on normal
force(Fn) and tangential force(Ft).
Cips concentration & Working gap

18. Effect of abrasive concentration on the normal force(Fn) and
tangential force (Ft) (carbonyl iron particles(CIPs)=40%, wheel
speed=300 rpm, working gap=1 mm).
Abrasive Concentration

19. Effect of wheel speed on normal force(Fn) and tangential
force(Ft) (carbonyl iron particles(CIPs)=40%,
abrasive=5%, working gap=1 mm).
Wheel Rotation

20.  Normal as well as tangential forces decrease with
increase in working gap; however, both forces increase
with increase in CIP concentration.
 Both forces increase with increase in abrasive particle
concentration up to 3.5% but after that they decrease
with further increase in abrasive particle concentration.
 Normal force increases with increase in wheel speed
but tangential force increases up to a certain wheel
speed beyond which it starts decreasing.

21. Experimental results of MRF (a) initial surface topography, and
(b) after finishing for 50 min
 The above figure shows nano-finishing of glass lenses for 50 min
using MRF process.
 This finishing process is capable to produce surface finish of the
order of 10–100nm peak to valley height, and 0.8nm RMS value in
finishing optical lenses .

22. High Accuracy
Enhances product quality and repeatability
Increased production rate, productivity, yield, and cost
effectiveness.
Stable in nature
Manufacture precision optics... better, faster, and cheaper.
Flexible and fast,
Optical glasses micro roughness of less than 10 angstroms rms.
Polishing tool is easily adjusted,
and conforms perfectly to the work piece surface,
No subsurface damage.

23.  High-quality fluids are expensive.
 Fluids are subject to thickening after prolonged use and
need replacing.
 Settling of ferro-particles can be a problem for some
applications.
 Not suitable for finishing internal and external surfaces
of cylindrical components.

24.  Obtain high-precision surfaces.
 Optical glasses, single crystals (calcium fluoride,
silicon…) and ceramics.
 Square and rectangular aperture surfaces such as
prisms, cylinders, and photo blank substrates.
 The nano diamond doped MR fluid removes edge
chips, cracks, and scratches in sapphire bend bars.
 High-aspect-ratio optics and substrates (thin film
filters, etalon substrates, semiconductor wafers).

25. High aspect ratio optics
Large face sheet
Sapphire Windows
APPLICATION EXAMPLES
Light weight Primary Mirror
Meter-Class Aspheres

26.  From the above discussion we can conclude that the
MRF is an effective super finishing process for optical
materials with variety shapes such as flat, spherical,
Concave, and convex.
 Surface finish up to nano meter level is achieved
without sub surface damage.

27.  QED technologies. www.qedmrf.com
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