Title of Invention | "A METHOD FOR MAGNETIC ABRASIVE FINISHING USING A PULSATING FLEXIBLE MAGNETIC ABRASIVE BRUSH " |
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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. |
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1990-del-2005-Abstract-(19-05-2011).pdf
1990-del-2005-Claims-(19-05-2011).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-Form-1-(19-05-2011).pdf
1990-del-2005-Form-2-(19-05-2011).pdf
1990-del-2005-Form-5-(19-05-2011).pdf
1990-del-2005-GPA-(19-05-2011).pdf
1990-del-2005-patition others.pdf
Patent Number | 255664 | ||||||||||||
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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:
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PCT International Classification Number | B24B 31/00 | ||||||||||||
PCT International Application Number | N/A | ||||||||||||
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