Title of Invention

"A METHOD FOR MAGNETIC ABRASIVE FINISHING USING A PULSATING FLEXIBLE MAGNETIC ABRASIVE BRUSH "

Abstract This invention relates to a method for magnetic abrasive finishing using a pulsating flexible magnetic abrasive brush comprising steps of mixing of ferromagnetic iron particles with an abrasive in a ratio of 3:2 to 4:1 by weight, attraction of the mixture thus obtained by a magnetic field in the finishing zone followed by joining with each other along the lines of magnetic field forming a flexible magnetic abrasive brush, pushing the brush against workpiece surface so as to develop finishing pressure to realize micro cutting by relative motion wherein the electromagnet is supplied with pulsed direct current such as herein described and also this invention relates to a method for magnetic abrasive finishing as claimed in claim 1, Wherein the device for magnetic abrasive comprising a finishing equipment (1), a pulse generator (2) and a dynamometer (3), the finishing equipment (1) having a coil (4), an iron core, a yoke, flat faced magnetic poles and a table wherein the electromagnet (4) comprising of a ferromagnetic center pole (6) with electrical coil surrounded by art outer shell (7).
Full Text DEVICE AND METHOD FOR ENHANCEMENT OF SUPERFINISHING
USING A PULSATING FLEXIBLE MAGNETIC ABRASIVE BRUSH
The present invention relates to a pulsating flexible magnetic abrasive
brush for use in superfinishing processes involved in the manufacture of
advanced engineering materials. The present invention also relates to a method
for the enhancement of superfinishing of advanced engineering materials by a
pulsating flexible magnetic abrasive brush.
Various components of advanced engineering materials such as silicon
nitride, aluminium oxide, and semiconductors in extremely low surface
roughness (few nano meters) and high form accuracy are in demand in advanced
industrial fields, especially in ultra precision manufacturing industries.
Conventional techniques are incapable to superfinish these materials. One of the
processes developed for this purpose was the magnetic abrasive finishing (MAP)
process. The applications of super finishing are in the finishing of bearings,
precision automotive components, shafts, artificial hip joints, and similar other
components.
The basic principle of magnetic abrasive finishing is that iron particles
mechanically homogeneously mixed with SiC abrasives in a certain ratio are
attracted by magnetic field in the finishing zone, and they are joined with each
other along the lines of magnetic field due to dipole-dipole interaction and
forming flexible magnetic abrasive brush (FMAB) which pushes against the work
piece surface to develop finishing pressure to realize micro cutting by relative
motion. The flexible means employed comprises a magnetic abrasive brush
formed as a single body which adapts the contour of workpiece surface being
finished.
FMAB behavior is related to the magnetic field. The field strength is
constant at a particular smooth direct current (D.C.) in a specified finishing zone
due to constant magnetizing energy. Hence, at a specified constant current, the
FMAB strength will remain the same and correspondingly the positions of
abrasive grains trapped in the matrix of iron particles get unchanged. The
trapped abrasive grains become dull in due course of time. But in the case of
pulsed D.C. supply, the field strength would be pulsating and hence the
formation and breaking of FMAB would take place at pulsed D.C. frequency.
Therefore, refreshment/jumbling of abrasive grains would take place which
brings new cutting edges of grains. Hence, material removal and surface finish
get enhanced significantly as compared to the smooth D.C. supply. It is felt that
pulsed current influences magnetic field behavior, FMAB, and abrasive grain
behavior within the finishing zone.
Most prior art work has focused on finishing characteristic using the
surface roughness profile as a measure by chopping off the direct current supply
to the magnet or using AC magnetic field. The idea of using pulsed DC current
to the electromagnet is to see the effect of formation and breaking of magnetic
brush in the finishing zone at different pulsed parameters. The configuration of
the brush basically governs the material removal and surface roughness. In
depth research findings in this direction have not been reported in the literature.
The present invention provides an improvement comprising a pulsating
flexible magnetic abrasive brush. Initial preliminary experimentation have been
conducted successfully to find out pulsed parameters affecting surface finish and
to know the process behavior. Then pulsed parameters were designed
statistically and experiments conducted to analyze finishing on the plane surface
of ferromagnetic work piece. The finishing mechanism of the invention was
tested and the in process behaviour of magnetic force was studied. The magnetic
force and cutting force, both being utilized in the finishing operation, have been
measured on-line by in-house designed and fabricated a precise force transducer.
This transducer uses a strain gauge signal conditioner unit and Lab view
software, a complete use of virtual instrumentation unit. The pulsed current
with different duty cycles and on-time, and their corresponding on-line force
behavior has been found helpful to understand the behavior of cutting edges of
the abrasive particles. The setup for MAP with Pulsating Magnetic Abrasive
Brush has been designed and fabricated. The schematic view of the set up is
shown in Fig. 1. The pulsed generator is connected across the electromagnet.
The pulsed voltage and current has been measured by 2-channels digital storage
oscilloscope.
Experiments were conducted as per the condition given below and
relationship between percentage change in surface roughness with duty cycles
for a constant on-time has been established as shown in Fig.2. The results show
that percentage change in surface roughness increases remarkably with increase
in duty cycles. It is justified as follows: the duty cycle of a single pulse is defined
as the ratio of on-time to the total pulsed time (on +off)-time. For a constant ontime,
if duty cycle increases off-time decreases. Hence, FMAB will get more time
to get deformed and again during on-time it will get formed. The formation and
breaking of brush increases in less duty cycle which promotes grains stirring
effect within FMAB resulting in increased intermittent microcutting. As a result,
material removal increases resulting in increased % change in surface roughness.
The atomic force micrographs (Fig.3a and 3b) show clearly the significant stirring
effect of the FMAB due to formation and breaking of the brush at pulsed
frequency.
Comparatively low forces act on the work surface. As a result the finish is
without surface defects
The finishing of advanced engineering materials by smooth flexible
magnetic abrasive brush (FMAB) is a developed process in recent past. The
abrasive grains trapped in iron matrix become dull in due course of time during
finishing. In the present invention, however, the grains are refreshed due to the
on and off nature of the pulsed current by setting pulsed parameters during
finishing resulting enhanced rate of surface finishing. To the best of the
applicants knowledge, such method has not been attempted in the art heretofore.
The basic principle of magnetic abrasive finishing is that iron particles
mechanically homogeneously mixed with SiC abrasives in a certain ratio are
attracted by magnetic filed in the finishing zone, and they are joined with each
other along the lines of magnetic field due to dipole-dipole interaction and
forming flexible magnetic abrasive brush (FMAB) which pushes against the work
piece surface to develop finishing pressure to realize micro cutting by relative
motion. Here flexible means the magnetic abrasive brush as a single body adapts
the contour of workpiece surface being finished.
In the method of the invention, the effect of formation and breaking of
flexible magnetic brush in the finishing zone at different pulsed parameters was
studied when a pulsed DC current was provided to the electromagnet. The
configuration of the brush basically governs the material removal and surface
toughness. During the work on the MAB process, it was observed that the rate of
finishing is comparatively low. This is believed to be due to the fact that abrasive
particles wear out and the same wornout particles are continuously in contact
with the workpiece, thereby reducing the rate of finishing. As a result, several
tests were carried out to devise methods to replace/refresh the abrasive grains
trapped in the FMAB during finishing in order to bring fresh particles in contact
with workpiece and in order to remove the material significantly faster from the
peaks of the workpiece resulting smoothened surface.
Finishing, cleaning, debutting and burnishing of metal and advanced
engineering material parts are the end operations on any products. The
derivable products from the invention can be used in high technology engineering
products such as precision industries including, aerospace, semiconductors, etc. The
process and device of the invention has an advantage over prior art processes such as
abrasive flow machining and MRAFF since, by adding/mounting an MAP
attachment to an existing machine like a vertical milling machine or drilling machine,
submicron finishing can be easily performed.
Turning now to Figure 1 which is a schematic representation of the device of
the invention, a pulsed power generator is connected in series to an electromagnetic
coil and through a magnetic pulse inducer to a 2-channel DSO, which in turn is
connected to a computational machine such as a computer. The electromagnet has a
coil and is preferably a C shaped electromagnet. A mixture of SiC and iron particles
agglomerate at the poles of the electromagnet and form flexible electromagnetic
brushes. The workpiece is provided below the poles and in contact with the flexible
electromagnetic brush. The workpiece to be finished is supported on a ring
dynamometer, which in turn is connected to a data acquisition mechanism through
signal conditioning unit. A voltage is applied through the pulsed power generator. As
described hereinabove, the application of DC pulses causes the SiC and iron particles
to constantly change positions thereby bringing fresh surfaces thereof in contact with
the workpiece, thereby ensuring that surface micromachining is maintained for a
longer period of time. The contact of fresh rough abrasive surfaces of the particles
forming the brush with the workpiece ensure that the finishing efficiency is
substantially maintained over a longer period of time. The signal conditioning unit
transmits profile data to the data acquisition means which then issues corresponding
instructions to the pulsed power generator to cease operation once desired finish
level on the workpiece is achieved.
Figure 2 is a graphical representation of the relationship between Ra and the
duty cycles at on time where on time is 2000 is JJs, the working gap is 1.5 mm and the
RPM is 200 for a time of 15 minutes.
Figures 3 (a) to (c) depict the surface of the workpieces after grinding but
before being subjected to the microfinishing process of the invention, after finishing
by smooth FMAB and after finishing with pulsating FMAB respectively. As is
evident, the finish achieved by pulsating FMAB is significantly improved over
finishing by smooth FMAB. This is essentially due to the fact that the application of a
pulsating DC current ensures that the flexible magnetic abrasive brush constantly
provides new surfaces of the abrasive particles to contact and finish the workpiece
surface.
The above disclosure is non-limiting, and variations and modifications are
possible without departing from the spirit and scope of the invention.





WE CLAIM;
1. A method for magnetic abrasive finishing using a pulsating flexible
magnetic abrasive brush comprising steps of:-
- mixing of ferromagnetic iron particles with an abrasive in a ratio of 3:2 to 4:1 by weight,
- attraction of the mixture thus obtained by a magnetic field in the finishing zone followed by joining with each other along the lines of magnetic field forming a flexible magnetic abrasive brush,
- pushing the brush against workpiece surface so as to develop finishing pressure to realize micro cutting by relative motion wherein the electromagnet is supplied with pulsed direct current such as herein described.
2. A method for magnetic abrasive finishing as claimed in claim 1,
wherein the. abrasive is selected from Silicon carbides, Aluminum
oxides, Cromium oxides and Diamond.
3. A method for magnetic abrasive finishing as claimed in claim 1 or
2, wherein the ferromagnetic iron particles are selected from pure
iron powder and carbonyl iron powder.
4. A method for magnetic abrasive finishing as claimed in claim 1,
wherein the workpiece is selected from Magnetic Materials and
Non-magnetic materials.

5. A method for magnetic abrasive finishing using a pulsating flexible magnetic abrasive brush substantially as herein described and illustrated.
6. A method for magnetic abrasive finishing as claimed in claim 1, wherein the device for magnetic abrasive comprising a finishing equipment (1), a pulse generator (2) and a dynamometer (3), the finishing equipment (1) having a coil (4), an iron core, a yoke, flat faced magnetic poles and a table wherein the electromagnet (4) comprising of a ferromagnetic center pole (6) with electrical coil surrounded by an outer shell (7).
7. A magnetic abrasive finishing as claimed in claim 6, wherein the dynamometer (3) is a ring type,
8. A magnetic abrasive finishing substantially as herein described and illustrated.

Documents:

1990-del-2005-Abstract-(19-05-2011).pdf

1990-del-2005-abstract.pdf

1990-del-2005-Claims-(19-05-2011).pdf

1990-del-2005-claims.pdf

1990-del-2005-Correspondence Others-(27-11-2012).pdf

1990-del-2005-Correspondence-Others-(11-03-2011).pdf

1990-del-2005-Correspondence-Others-(19-05-2011).pdf

1990-del-2005-correspondence-others.pdf

1990-del-2005-description (complete).pdf

1990-del-2005-Drawings-(19-05-2011).pdf

1990-del-2005-drawings.pdf

1990-del-2005-Form-1-(19-05-2011).pdf

1990-del-2005-form-1.pdf

1990-del-2005-Form-2-(19-05-2011).pdf

1990-del-2005-form-2.pdf

1990-del-2005-form-26.pdf

1990-del-2005-form-3.pdf

1990-del-2005-Form-5-(19-05-2011).pdf

1990-del-2005-form-5.pdf

1990-del-2005-GPA-(19-05-2011).pdf

1990-del-2005-patition others.pdf


Patent Number 255664
Indian Patent Application Number 1990/DEL/2005
PG Journal Number 11/2013
Publication Date 15-Mar-2013
Grant Date 13-Mar-2013
Date of Filing 27-Jul-2005
Name of Patentee INDIAN INSTITUTE OF TECHNOLOGY, KANPUR
Applicant Address KANPUR 208 016, UTTAR PRADESH, INDIA.
Inventors:
# Inventor's Name Inventor's Address
1 VIJAY KUMAR JAIN MECHANICAL ENGINEERING DEPARTMENT, INDIAN INSTITUTE OF TECHNOLOGY KANPUR 208 016, INDIA.
2 VIDYALA RAGHURAM MECHANICAL ENGINEERING DEPARTMENT, INDIAN INSTITUTE OF TECHNOLOGY KANPUR 208 016, INDIA.
3 DHIRENDRA KUMAR SINGH MECHANICAL ENGINEERING DEPARTMENT,INDIAN INSTITUTE OF TECHNOLOGYKANPUR 208 016, INDIA.
PCT International Classification Number B24B 31/00
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 NA