NANO FINISHING TECHNIQUES

NANO FINISHING TECHNIQUES

Presented By –Arijeet Mohapatra

B.Tech. (Mech Engg.)

Submitted to –Professor K.K.DasburmaProfessor K. N.PanigrahiProfessor R.R.SwainMechanical Engg. Department

What is Nanofinishing?Nanofinishing is ultra precision finishing process which

is developed for obtaining nanometer order surface finish.

Nanotechnology was first used to provide ultraprecision machining capabilities in 1 nm order.

Need for NanofinishingTraditional finishing processes are incapable of producing

required surface characteristics to meet demand of nanotechnology.

Electronics and computer industries are demanding higher precision for large devices and high data packing densities.

To improve interchangeability of components, improve quality control and longer wear/fatigue life.

To name a few, Magnetic Abrasive finishing (MAF), Magnetorheological finishing (MRF), Elastic Emission Machining (EEM), Magnetic Float Polishing (MFP) and Ion Beam Machining (IBM).

ULTRA PRECISION FINISHING PROCESSES

FINISHING PROCESS Ra VALUE (nm)Magnetic Abrasive finishing(MAF)

7.6

Magnetic FloatPolishing (MFP) with CeO2

4.0

MagnetorheologicalFinishing (MRF) with CeO2

0.8

Elastic EmissionMachining (EEM) with ZrO2 abrasives

<0.5

Ion Beam Machining (IBM) 0.1

Magnetic Abrasive Finishing (MAF)

Ferromagnetic particles sintered with fine abrasive particles (Al2O3, SiC, Cubic Boron Nitride Powder or diamond) are called ferromagnetic abrasive particles (or magnetic abrasive particles).

Homogeneously mixed loose ferromagnetic and abrasive particles are used in certain applications.

Magnetic field is applied across gap between workpiece surface and rotating electromagnet pole.

Magnetic abrasive grains combined to each other magnetically form flexible magnetic abrasive brush.

Force due to magnetic field is responsible for causing abrasive penetration inside workpiece while rotation of magnetic abrasive brush results in material removal in form of chips.

Magnetic Abrasive Finishing (DIAGRAM)

Magnetic Abrasive Finishing (MAF)(contd.)

Magnitude of machining force caused by magnetic field is very low, a mirror like surface finish (Ra value in the range of nano-meter) can be obtained.

Controlling exciting current of magnetic coil precisely controls machining force.

Good quality finish on internal and external surfaces of tubes as well as flat surfaces made of magnetic or non-magnetic materials.

The surface finishing, deburring and precision rounding off the workpiece can be done simultaneously.

MAF uses this magnetic abrasive brush for surface and edge finishing.

The magnetic field retains the powder(CUBIC BORON NITRIDE POWDER) in the gap, and acts as a binder causing the powder to be pressed against the surface to be finished.



Results were reported in the literature of finishing stainless steel rollers using MAF to obtain final Ra of 7.6 nm from an initial Ra of 0.22 μm in 30 seconds.

ELECTRO-MAGNET

CYLINDRICAL WORKPIECE

MAGNETIC ABRASIVE BRUSH

APPLICATIONMagnetic abrasive finishing (MAF)

processes have been developed for a wide variety of applications including the manufacturing of medical components, optics, dies and molds, electronic components and mechanical components.

Magnetorheological FinishingUses Magnetorheological (MR) fluid- suspension of

micron sized magnetizable particles (e.g.Carbonyl iron) dispersed in non-magnetic medium (mineral oil, water,silicone oil).

On Applying Magnetic field to MR suspension, particles acquire dipole moments & aggregated into chains of dipoles.

N.Y. Rochester, has developed a technology to automate the lens finishing process known as Magnetorheological Finishing.

Magnetorheological Finishing (contd..)

•Surface smoothing, removal of sub-surface damage, and figure correction are accomplished by rotating the lens on a spindle at a constant speed while sweeping the lens about its radius of curvature through the stiffened finishing zone .

Material removal takes place through the shear stress created as the magnetorheological polishing ribbon is dragged into the converging gap between the part and carrier surface.


.


Zone of finishing is restricted to a spot.

Most efficient & for High precision finishing of optics.

MRF makes finishing of free form shapes possible for first time.

Applications: high precision lenses include medical equipment such as endoscopes, military's night vision equipment like infrared binoculars.

•Resistance to applied shear strain by chains is responsible for material removal

ADVANTAGES:

Elastic Emission Machining

Uses ultra fine particles to collide with workpiece surface.

Finish surface by atomic scale elastic fracture & directly by removing atoms & molecules from surface without plastic deformation.

Workpiece is submerged in slurry of abrasive particles (ZrO2 or Al2O3) and water.

Polyurethane ball(56 mm dia) mounted on shaft, driven by motor, is used to apply working pressure.

Material removed by erosion of surface atoms by bombardment of abrasive particles.

Elastic Emission Machining (contd..)



It is able to remove material at the atomic level by mechanical methods.

Surface roughness as low as 0.5 nm have been reported on glass.

Ceramics are extremely sensitive to surface defects resulting from grinding and polishing processes. Fatigue failure of ceramics is driven by surface imperfections.

For this gentle and flexible polishing conditions like low level of controlled forces and use of abrasives softer than work material are required.

The schematic diagram of the magnetic float polishing apparatus used for finishing advanced ceramic balls is shown in Fig. 5.

Magnetic Float Polishing

A magnetic fluid containing fine abrasive grains and extremely fine ferromagnetic particles in a carrier fluid such as water or kerosene fills the aluminium chamber.

A bank of strong electromagnets is arranged alternately north and south below the chamber.

On the application of magnetic field the ferro fluid is attracted downward towards the area of higher magnetic field and an upward buoyant force is exerted on non-magnetic material(abrasive grains, ceramic balls, and acrylic float) to push them to the area of lower magnetic field.

Drive shaft is fed down to contact the ball and presses them down to reach the desired force level.

The balls are polished by the relative motion between the balls and the abrasives under the influence of buoyant force and resistance.

Both higher material removal rate and smoother surface in this polishing method, are attained by stronger magnetic field and finer abrasives.

Conventional polishing of ceramic balls takes considerable time(12-15days) to finish a batch of ceramic balls because of low polishing speeds and use of expensive diamond abrasive at high loads can result in scratches, and micro cracks.

Magnetic Float polishing is used to finish 9.5 mm diameter Si3N4 balls.

The surface finish obtained was 4 nm Ra and 40 nm Rmax. Finished surfaces relatively free of scratches, micro cracks, etc. were obtained.

Ion Beam Machining (IBM)The system consists of an ion source that

produces sufficient intense beam of ions, for the removal of atoms from the work surface by impingement of ions.

A heated tungsten filament acts as the cathode from which the electrons are accelerated by means of a high voltage(1 kV to 100kV) towards the anode.

Once the ions strike the machined surface obliquely, the atom ejection occurs due to the collision.

At higher energies sufficient momentum causes removal of several atoms from the surface.

Many microscopic damage centers will result from the energetic displacements of the atoms. Clearly it is not desirable from surface quality point of view. The low energy case is more ideal.

The sputtering yield S is defined as the mean number of atoms sputtered from the target surface per incident ion.

The yield and hence, the machining rate depends on the binding energy of atoms, in the material being machined.

The etch rate V(θ) in atoms per minute is given by :

where, n = atomic density of the target material in atoms/cm³,S(θ) = yield, atoms per ion andθ = ion beam at an angle θ to the normal

Ion beam machining is ideal process for nano-finishing of high melting point and hard brittle materials such as ceramics, diamonds etc.

As there is no load on the workpiece while finishing, it is suitable for finishing of very thin objects, optics and soft materials such as CaF2(calcium fluoride).

Argon ion beam of an energy E=10keV was used to sharpened the styli to the tip radius of 10 nm.

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NANO FINISHING TECHNIQUES