advanced fine finishing process
TRANSCRIPT
Mechanical Engineering Dept.L D College of Engineering, Ahmedabad.
Gujarat Technological University, Ahmedabad.
ADVANCED FINE FINISHING PROCESS ABRASIVE FLOW MACHINING(AFM)
MAGNETIC ABRASIVE FINISHING (MAF)
MAGNETO RHEOLOGICAL ABRASIVE FINISHING
ABRASIVE FLOW MACHINING (AFM)
Introduction to AFM Abrasive flow machining (AFM) was developed by Extrude Hone Corporation, USA in 1960.
AFM is used to deburr, radius and polish difficult to reach surfaces by extruding an abrasive
laden polymer medium with very special rheological properties.
It is widely used finishing process to finish complicated shapes and profiles.
The polymer abrasive medium which is used in this process, possesses easy flow ability, better
self deformability and fine abrading capability.
Layer thickness of the material removed is of the order of about 1 to 10 μm. Best surface finish
that has been achieved is 50 nm and tolerances are +/- 0.5 μm.
Process description and Principle
Fig. 1.1 Principle of material removal mechanism in two way AFM process.
Fig. 1.2 Schematic diagram of the action of Single active abrasive grain.
Classification AFM machine There are three types of AFM machines that have been reported in the literature:
1) One way AFM,
2) Two way AFM and
3) Orbital AFM.
Commonly used AFM is Two-way AFM in which two vertically opposed cylinders extrude
medium back and forth through passages formed by the workpiece and tooling.
One way AFM process One-way flow AFM processing pushes
abrasive media through the work piece in
only one direction, allowing the media to
exit freely from the part.
Fig.1.3 Unidirectional AFM process
The advantages of One Way AFM Faster cycle processing
Easy clean-up
Media temperature control generally not required
Able to process larger parts
Simpler tooling and part change-over
Accurately replicates air or liquids natural flow
Does not encapsulate workpart in media
Two way AFM process Two way AFM machine has two hydraulic cylinders and two medium cylinders. The medium is
extruded, hydraulically or mechanically, from the filled chamber to the empty chamber via the
restricted passageway through or past the workpiece surface to be abraded (Fig.1.1).
Typically, the medium is extruded back and forth between the chambers for the desired fixed
number of cycles. Counter bores, recessed areas and even blind cavities can be finished by using
restrictors or mandrels to direct the medium flow along the surfaces to be finished.
Advantages of Two-Way AFM Excellent process control
Can finish both ID and OD of component
Good control of radius generation
Fully automated system capabilities
Faster setup & quick-change tooling
Faster change-over of media
Orbital AFM process Surface and edge finishing are achieved rapid, low-amplitude, oscillations of the work piece
relative to a self-forming elastic plastic abrasive polishing tool.
The tool is a pad or layer of abrasive-laden elastic plastic medium (similar to that used in two
way abrasive flow finishing), but typically higher in viscosity and more in elastic.
Fig.1.4 Orbital AFM before start of finishing.
Fig.1.5 Orbital AFM while finishing
Mechanism of material removal Two modes of abrasive wear, micro-ploughing and micro-cutting, have been identified
as the mechanisms of removal in AFM.
In micro-ploughing, surface peaks are smeared and plastically deformed, resulting in
‘‘leveling out’’ of surface asperities. No volume loss takes place in this mode of removal.
Ridges are also formed adjacent to the grooves created by abrasive particles’ sliding
path.
On the other hand, in micro-cutting, abrasive particles act as single-point cutting
tools, indenting and removing material in the form of microchips.
In both forms of abrasive wear, scratches are characterized by continuous scratches.
Classification of major AFM research areas
Process Input Parameters of AFM
Extrusion Pressure
Number of cycles
Grit composition and Type
Tooling
Fixture design
Operating range of AFM
Easy flowability
Better self deformability
Fine abrading capability
Layer thickness of material removed is, order of about 1μm to 10 μm
Best surface finish that has been achived as 50nm and tolerances +/- 0,5 μm
Properties of AFM
Deburring , radiusing, and polishing are performed simultaneously in a single
operation
AFM can produce true round radii even on complex edges
Reduces surface roughness by 75 to 90 % on cast and machined surfaces
AFM can process dozens of holes or multiple passages parts simultaneously
with uniform results
Monitoring of AFM processFor online monitoring of material removal and surface roughness in AFM process,
Williams and Rajurkar applied acoustic emission technique.
They developed a stochastic model of AFM generated surfaces by using Data
Dependent Systems (DDS) methodology.
It was established in their research that AFM finished surface profiles possess two
distinct wavelengths, a large wavelength that corresponds to the main path of abrasive
while the small wavelength is associated with the cutting edges.
AFM machining and monitoring system
(a) AFM machining and monitoring setup;
(b) schematic of the process monitoring system.
Application of AFM Automotive
Aerospace
Medicine
Dies and Moulds
Fig. 1.7 Surface finish improvement before and after on (a) internal passages within turbine engine diffuser (b)
Medical implants (c) complex automotive engine parts.
AFM in Aerospace Industry Improved surface quality
Enhanced high cycle fatigue strength
Optimized combustion and hydraulics
Increased airflow
Extended component life
AFM in Automotive Industry Enhanced uniformity and surface quality
of finished components
Increased engine performance
Increased flow velocity and volume
Improved fuel economy and reduced
emissions
Extended work piece life by reducing
wear and stress surfaces
Fig. : Polishing and blending
the internal surfaces
Figure : Grains in the same
direction to increase flow rates.
AFM in Dies and mold Industry Reduced production costs
Increased production throughput
Enhanced surface uniformity, finish and
cleanliness
Improved die performance and extend life of
dies and molds
AFM in Medical Industry Eliminate the surface imperfections where dangerous
contaminates can reside
Improved functionality, durability and reliability of medical
components
Enhanced uniformity and cleanliness of surfaces
Extended component life
Process limitations Geometries such as blind holes remain difficult to be finished effectively by AFM.
AFM’s media are also governed by the fluid flow properties, leading to difficulty in exerting
uniform finishing forces on complex internal surfaces.
Preferential flow over more restricted areas results in non-uniform finishes.
Furthermore, abrasive particle embedment onto the workpiece surface had been reported by
various researchers, thereby raising contamination issues. This could be undesirable in parts
where high material purity of the component is required.
Summary of AFM Possible to control and select the intensity and location of abrasion
Produces uniform, repeatable and predictable results on an impressive range of finishing operations.
Maintain flexibility and jobs which require hours of highly skilled hand polishing can be processed in a
few minutes
Process used in aerospace, medical and automobile industries
Better surface roughness values and tight tolerances.
Disadvantage of this process is low finishing rate
Better performance is achieved if the process is monitored online.
Improve surface quality
Reduction in Friction
Eliminate imperfection
Magnetic Abrasive Finishing (MAF)
Introduction to Magnetic Abrasive Finishing (MAF) Various industrial applications require very high surface finish upto the range of nanometers or even above.
Presently, it is required that the parts, used in manufacturingsemiconductors, atomic energy parts, medical instruments andaerospace applications, have a very fine surface roughness.
Amongst them, vacuum tubes, wave-guides and sanitary tubesare difficult to be polished by conventional finishing methods suchas lapping, because of their shapes.
The technology for super finishing needs ultra clean machiningof advanced engineering materials such as silicon nitride, siliconcarbide, and aluminum oxide which are used in high- technologyindustries and are difficult to finish by conventional grinding andpolishing techniques with high accuracy, and minimal surfacedefects, such as micro cracks.
Therefore, magnetic abrasive finishing (MAF) process has been recently developed for efficient
and precision finishing of internal and flat surfaces.
This process can produce surface finish of the order of few nanometers.
In addition, MAF possesses many attractive advantages, such as self-sharpening, self-
adaptability, controllability, and the finishing tool requires neither compensation nor dressing.
Magnetic abrasive finishing (MAF) is a high-precision nontraditional finishing process in
which the finishing forces are controlled by a magnetic field. Magnetic abrasive particles
supplied to a work piece are influenced by magnetic poles, thus forming a flexible magnetic
abrasive brush.
Process description and principleWhen current is supplied to the coils around themagnetic yoke, magnetic abrasive particlesconglomerate according to magnetic field distributionat the finishing zone, acting as a flexible brush.
the work piece is also vibrated axially at amplitude of10–50mm and frequency between 5 and 20 Hz
With repeated revolutions, a smooth inner surfacewould be generated. To prevent excessive frictionalforce, lubricating fluid such as oil could also be fed intothe passage during finishing.
The material is removed in the form of fine abrasion with increasing machining time.
Process parameters
Magnetic abrasive mixThe modern mixed-type magnetic abrasive was invented to obtain a balance between
magnetic susceptibility and abrasion properties of magnetic abrasive conglomerates.
Large ferromagnetic particles (100–500mm) are responsible to produce magnetic force and
finishing pressure; while hard abrasive particles (5–20mm) are responsible for abrading Workpiece surface and removing material.
In general, as ferromagnetic particle size increases, finishing force per particle increases, thusresulting in increasing MRR. However, beyond particle size of 330mm, excessive materialremoval occurs, which negatively impacts minimum Ra achievable. On the other hand, smallerabrasive particle size leads to more particles being sintered on each ferromagnetic particle.
MAGNETIC ABRASIVE FINISHING MATERIAL PREPARATION METHODSSINTERING:
It’s a method for making objects frompowder.
By heating the material in a sintering furnacebelow its melting point (solid state sintering).
Traditionally used for manufacturing ceramicobjects & in the field of powder metallurgy.
ADHESIVE BONDING:
A special type of adhesive is required forproviding a strong bond between magneticand abrasive component.
The amount of adhesive in mixture ofabrasive and Ferro magnetic components wasdecided in such a way that adhesivecompletely wets the mixture and at the sametime the mixture should not behave like afluid.
Types of Magnetic Abrasive FinishingMAF with permanent magnet
MAF with Direct Current
MAF with Alternating Current
MAF with permanent magnet
the work piece is kept between the twopoles of a magnet.
The working gap between the work pieceand the magnet is filled with magneticabrasive particles.
A magnetic abrasive flexible brush (MAFB) isformed, acting as a multipoint cutting tool,due to the effect of the magnetic field in theworking gap.
MAF with Direct Current
In MAF operation, work piece is keptbetween the two magnets.
The magnetic poles N & S were placed face toface with their axes crossing at right angle witha brass pipe in the configuration as shown infigure.
The experimental setup has majorcomponents like electromagnet (10 k Gauss),control unit, D.C. motor, variable D.C. supply.
MAF with Alternating Current
The rotating magnetic field obtained by
electrifying three coils arranged in the
directions at intervals of 120 degrees with
three phase AC current for internal finish
cylindrical work pieces.
Process capability and applicationsMAF offers mirror-like surface finishing
capabilities as roughness could be reduced
down to 10nm Ra. It is a high-precision
process whereby form accuracy is not
adversely affected. The concept of internal
MAF was first demonstrated on difficult-to-
access area of the internal surface of a clean
gas bomb.
Study on Magnetic Abrasive Finishing Process using Low - Frequency Alternating Magnetic Field
Fig. shows a schematic of the plane magnetic abrasive
finishing process using alternating magnetic field.
The tray contains the compound magnetic grinding fluid
(oily grinding fluid, iron powder and abrasive), the lower
is the magnetic pole and the upper is the work piece.
After electromagnetic coil entering alternating current,
alternating magnetic field will be produced.
Experimentation ( Setup )
Experimentation ( Condition )Experimental conditions
Work piece SUS304 stainless steel plate with the size of80mm×90mm×1mm
Finishing time 60 min
Abrasive Al₂O₃, 0-1[μm] in mean dia: 0.3[g]
Cutting fluid Neat cutting oil (Honilo 988): 0.8[ml]
Feed speed of mobile stage 260 [mm/min]
Rotational speed of magnetic pole 350 [r/min]
Magnetic field Type 1:Direct magnetic field: 1.9[A].Type 2:Alternating magnetic field: 1.9[A]Current frequency :3[Hz]
Experimental results and discussion.
3D photographs of polished surfaces before and after finishing By DC
3D photographs of polished surfaces before and after finishing By AC
Experimental ConclusionI. In the case of using this experimental setup MAF process using low frequency alternating
magnetic field may obtain a smoother and more uniform finished surface than that of direct
magnetic field.
II. Based on analysis of the mechanism of increasing material removal on MAF process using
alternating magnetic field, we can calculate that material removal in alternating magnetic
field is approximately 2.05 times than that of direct magnetic field in this experimental
setup, and the results of prediction and calculation are verified by finishing experiments
Advantages & Applications of MAFADVANTAGES
I. Minimizes the micro-cracks and surface
damage of work piece.
II. MAF is able to produce surface roughness of
nanometer range with hardly any surface
defects .
III. The flexible magnetic abrasive brush (tool)
requires neither compensation nor dressing.
APPLICATIONS
I. Non -ferromagnetic materials like stainless steel, brass and aluminum.
II. Ferromagnetic materials like steels.
III. Finishing of bearing.
IV. Aerospace components.
V. Electronics components with micro meter or sub micrometer ranges.
Process limitationsDespite the promise of producing mirror-like surface, MAF’s biggest limitation lies in the
restriction on the materials that are suitable to be processed. Surface finishing is negligible on
ferromagnetic materials such as nickel and cobalt alloy. This is due to the work piece being
magnetized in the presence of magnetic field, thus attracting magnetic abrasive particles to it
strongly. So no any relative motion between magnetic abrasive particles and work piece surface.
Complicated internal features such as fins and protuberances would render MAF inefficient as
magnetic abrasive particles are unable to navigate around these features. However, these
limitations could be stretched by further research effort. More experimental studies are needed
to extend understanding and fully realize the potential of this finishing process.
Concluding remarksMAF for internal surfaces is a process with vast potential. Finishing force can be controlled
locally by altering the external magnetic field distribution. This is not achievable on AFM and
FBM as local flow manipulation is not possible. With very fine surface finish produced and its
capability on very small channels, MAF could find applications in precision finishing of most
internal passages.
Magneto-Rheological Abrasive Finishing
Introduction to Magneto-Rheological Abrasive FinishingIn magneto-rheological abrasive finishing abrasive mixed with magneto-rheological (MR) fluid is
used. Kordonski and Jacobs (1996) developed a setup in which magnetically stiffened magneto-
rheological fluid mixed with abrasives is made to flow over a moving flat rigid wall and the
polishing happens at a converging gap formed by the surface to be finished and a moving wall.
Now it finds an interesting industrial application in polishing of optical lenses.
Introducing the abrasive mixed MR fluid, the relative motions between the work piece and
abrasive medium are imparted in different ways; using reciprocation, rotation or combination of
both.
Magneto-Rheological Abrasive Finishing setup
History of MR FluidMagnetorheological (MR) fluids, invented by Rabinow in late 1940s, belong to a class of smart
controllable materials whose rheological behavior can be manipulated externally by the application of
some energy fields . These applications include shock absorbers, damping devices, clutches, brakes,
actuators, and artificial joints.
MR fluid works as polishing tool.
MRF uses MR fluid which is invented by Rabinow in late 1940s consist of
CIP (Magnetic)
Abrasive Particle (Non-magnetic)
carrier liquid (Oil or water)
additives (glycerol,grease)
Application & Limitation APPLICATION
MRF has been used for finishing a large variety of brittle material ranging from optical glasses to hard crystals.
LIMITATION
Internal and specially complex surfaces can’t be finished.
Magnetorheological abrasive flow finishing process (MRAFF)
• In order to maintain the versatility of Abrasive Flow Machining process and at the same time
introducing determinism and controllability of rheological properties of abrasive laden medium, a
new hybrid process termed as “Magnetorheological Abrasive Flow Finishing (MRAFF)” is used.
• It is deterministic process.
• Any complex geometries can be finished by this process.
• MRAFF process has the capability of finishing complex internal geometries up to nanometer level.
It imparts better control on the process performance as compared to AFM process.
• In MRAFF process, a magnetically stiffened slug of magnetorheological polishing fluid is extruded
back and forth through or across the passage formed by work piece and fixture. Abrasion occurs
selectively only where the magnetic field is applied across the work piece surface, keeping the
other areas unaffected. The mechanism is shown in Fig.
Comparison of surface before and after MRAFF(for 200 cycles at B = 0.574 T)
INITIAL SURFACE BEFORE MRAFF FINAL SURFACE AFTER MRAFF
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