Title of Invention

"AN ABRASIVE FLOW FINISHING DEVICE"

Abstract

An abrasive flow finishing device and a process of abrasive flow finishing comprising atleast a pair of hydraulic unit namely hydraulic cylinder, each of which is connected to MRP-fluid cylinder, an electromagnet coil disposed on either side of a workpiece fixture provided between the MRP-fluid cylinders wherein the cylinders are housed in a frame and the workpiece fixture is attached to a workpiece.Fig.

Full Text

MAGNETORHEOLOGICAL ABSRASIVE FLOW FINISHING PROCESS AND DEVICE THEREFOR The present invention provides a magnetorheological abrasive flow finishing process for the finishing of metals and non-metals with close tolerances as well as a device therefore. Precise control of finishing forces is an important consideration for fine finishing of metals and non-metals with close tolerances and without damaging surface topography. The major bottleneck hi existing finishing technologies lies hi their incapability of controlling abrading forces, hence final surface finish. The nature and strength of bonding material used to hold the abrasive particles together determines the extent of abrasion and quality of the finished surface. Advance fine finishing processes hi which efforts were made to precisely control and abrading forces are Magnetic Abrasive Finishing (MAP), Magnetic Float Polishing, (MFP), Magnetorheological Finishing (MRF) and Abrasive Flow Machining (AFM). In MAP, MRF and MFP, the magnetic field is used to control the abrading forces, but the applications of these processes are limited to specific simple geometries only due to restriction on relative movement of finishing medium and workpiece. These are incapable of finishing any geometry by allowing abrasive laden polymetric medium to flow over it. In AFM, the medium acts as complaint lap and overcomes shape limitation inherent in almost all traditional finishing processes. As abrading forces hi AFM process mainly depend on rheological behaviour of polymeric medium, which is least controllable by external means, hence lacks determinism. MRF process was developed for polishing optical flats, spheres and aspheres up to nanometer level using slurry comprised of aqueous MR-fluid and cerium oxide abrasives. The present invention provides a new precision finishing process based on both magnetic and rheological abrasive flow finishing. The process of the invention has been termed Magneto-Rheological Abrasive Flow Finishing (MRAFF), for superfinishing of complex internal and external metallic as well as non-metallic surfaces in nanometer range using specially prepared Magneto-Rheological Polishing (MRP) fluid. The MRP-fluid used is comprised of carbonyl iron powder particles and silicon carbide abrasives dispersed in the viscoplastic base of grease and heavy paraffin liquid. This smart fluid exhibits change in its rheological properties, hence bonding forces on abrasive particles, on the application of external magnetic field. The smart controllable behaviour of MRP-fluid provides better inprocess control of finishing forces on abrasive particles and final surface finish by controlling the magnetizing current in the electromagnets used. A hydraulically powdered MRAFF machine consists of two MRP-fluid cylinders, two hydraulic actuators, electromagnet, fixture and supporting frame is designed, developed and fabricated by the inventors. Experiments were successfully conducted on stainless steel workpieces to study the process performance and results are quite encouraging. Due to the unique characteristic of the process to extrude the MRP-fluid through the passage formed by workpiece and fixture, there is no limitation on geometry to finish. Apart from it, there is selective abrasion on surfaces where magnetic field is present preventing wear and tear of machine components. Abrasive Flow Machining (AFM) and Magnetorheological Finishing (MRF) processes are two existing process whose limitation are overcome hi the process of the invention. AFM was developed by Extrude Hone Corporation, USA in 1960 to deburr, polish, radius difficult to reach surface and edges of critical aircraft hydraulic and fuel system components. It works on principle of extruding abrasive laden viscoelastic polymeric medium through passage formed by workpiece surface and specially designed fixture. Researchers worked on AFM process have unanimously agreed on considering viscosity as one of the main process parameter and have found that the viscosity of abrasive laden medium temporarily rises hi restricted passages and significantly affect the finishing performance of the process. Depending on the flow pattern, for uniformly abrading the walls of large passages, more viscous medium is required as compared to radiusing edges and finishing small passages. It is also emphasized that rheological properties of the abrasive laden medium has significant role to play during finishing operation. But it is irony that the most significant parameter of AFM is least controllable. The viscosity of abrasive medium in AFM process depends upon the shape of passage involved; hence abrasion can not be controlled by any external means. It varies according to the workpiece shape. Another difficulty associated with abrasive laden polymeric medium is hi uniformly mixing of abrasives in it due to high viscosity of base viscoelastic polymer. The inventors were familiar with all these limitations as part of their research work on AFM process hi the past. Another process bear close resemblance with the present invention is Magnetorheological Finishing (MRF). MRF process was developed and brought to production stage by Center for Optics Manufacturing (COM) Rochester, USA for finishing high precision lenses, ceramics and semiconductor wafers. They used aqueous magnetorheological fluid with cerium oxide abrasives as a complaint replacement for the conventional rigid polishing lap. In the region where the workpiece surface and the magnetorheological polishing (MRP) fluid are brought hi contact, because of the applied magnetic field, a shear flow of Bingham plastic MRP fluid occurs through the gap resulting in material removal. Due to high magnetic flux density hi polishing zone, a polishing spot formed on the workpiece moves relative to its surface correcting surface errors by removing asperities. The dwelling time of workpiece hi moving MRP fluid ribbon determines the polishing characteristics. The application of MRF process is limited to finishing flat, spherical and aspherical external surfaces only because of its mechanism of action by dwelling workpiece in moving MRP fluid ribbon. It is incapable of finishing internal passages or complex geometries due to biggest limitation on relative movement of abrasives hi MR-fluid to workpiece surface. Also the standard MR polishing fluid compositions are effective for finishing optical glasses, glass ceramics, plastics and some non-magnetic metals. They have very little effect on hard materials. The MRAFF process of the invention overcomes the disadvantages of the prior art process and relies on extrusion of specially prepared magnetorheological polishing (MRP) fluid through passage formed by workpiece surface and fixture hi the presence of externally controlled magnetic field. Magnetorheological polishing fluid was prepared indigenously by dispersing carbonyl iron particles (CIPs) of size~ 18 jam and black silicon carbide abrasives of grit size 800 in viscoplastic base medium of heavy paraffin liquid and APS grease. Experiments were conducted on stainless steel workpieces to study the effect of magnetic field strength on change in surface roughness (Ra) and the results (Fig. 6) were quite encouraging and as per expectations. The improvement hi surface finish is higher at high magnetic field strength due to the increased bonding strength of carbonyl iron particle chains around abrasive particles trapped in between them. Magnetorheological Abrasive Flow Finishing (MRAFF) process was developed for super finishing of internal geometries of hard materials. This process relies for their performance on magnetorheological effect exhibited by carbonyl iron particles along with abrasive particles hi non-magnetic viscoplastic base medium. The extent of finishing action depends on radial and tangential forces coming on abrasive particles due to carbonyl iron particles (CIPs) arranged hi columnar structure in the presence of external magnetic field. The effects of abrasives and CIPs size on surface finish improvement were investigated. Experiments were conducted on stainless steel work pieces with different combinations of CIP and SiC particles in MRP-fluid for same volume concentration. The CIP chain structures were also observed microscopically to understand the chain formation and alignment around abrasive particles on the application of external magnetic field. Magnitudes of the forces on abrasive particles were then calculated and change in surface roughness model was developed to simulate final surface roughness. The improvement in surface finish hi case of MRP-fluid with CIP of average diameter 18 um for all combination of SiC particle size is more than CIP of diameter 3.5 um. The reduction hi surface roughness value for same CIP size decreases with decrease hi SiC particle size. The possible structure for all combination of CIP and SiC particle sizes are determined and surface roughness profile is generated after calculating forces coming on single SiC particle. The results are hi close agreement with the experimental values. For the same volume concentration of SiC and CIPs hi MRP-fluid, their relative size plays an important role in finishing action during MRAFF process. The bonding strength of CEP around SiC particles to a large extent is governed by the arrangement of CIPs hi the vicinity of SiC particles hi fluid. In the description of this invention, the following nomenclature has been adopted: //0 Magnetic permeability of free space, H m"1 ay Yield point stress of stainless steel workpiece in shear, Pa Ty Fluid shear stress, Pa %m Magnetic susceptibility of carbonyl iron particles (CIPs), m3/kg a Spacing between two abrasive particles passing over workpiece, m A Total projected area of spherical abrasive gram, m2 A Proj ected area of embedded portion of abrasive in the workpiece, m2 B Magnetic flux density, T DCJP Carbonyl iron particle diameter, m Df Fixture inner diameter in finishing zone, m Dp MRPF cylinder inner diameter, m Fm Magnetic force on CIP in external magnetic field, N Normal force on abrasive particle, N Shear force on abrasive particle, N H Magnetic field strength, A/m I Magnetizing current, A L Length of electromagnet coil, m Le MRP-fluid extruded (slug) length, m Ls MRPF cylinder stroke length, m Lspan CIP chain's spanning length from one end to another, m m Mass of CIP, kg n Number of turns per unit length, m"1 N Number of abrasive grains in a line in a stroke chains Number of chain ends per unit mm2 of workpiece surface area, mm"2 Nap Numbers of iron particles in a chain Ng Number of active abrasive grains in one stroke Nv Number of particles in volume V of MRP-fluid /; Core radius of electromagnet coil, m r2 Outer radius of electromagnet coil, m Rnormai Reaction force on abrasive particle due to Fn0nnai Rshear Reaction force on abrasive particle due to FShear t Depth of indentation, m V Volume of MRP-fluid, m3 VCJP Volume of a CIP particle, m3 jc Distance from pole face, m Yt Ordinate of roughness profile data, mm The ultra precision finishing technologies have grown rapidly over recent years, and have tremendous impact on the development of new products and materials. With the advent of these new materials, manufacturing engineers are facing challenge of machining and finishing these materials to meet their functional requirements. The available traditional and advanced finishing processes alone are incapable of producing desired surface characteristics on internal geometries, and in exercising in-process control on finishing action. Abrasive Flow Machining (AFM) process was developed to finish internal complex geometries by allowing abrasive laden polymeric medium to flow over it under pressure. The abrading forces in AFM process are function of viscosity of viscoelastic polymeric base medium, which is very difficult to control during operation. This lacks determinism in the control of finishing action. In another process developed for automated lens finishing, Magnetorheological finishing (MRF), external magnetic field is used to control the Theological properties of polishing medium, hence add determinism in controlling generated surface topography during finishing. The present applications of MRF process are limited to flat, spherical and aspherical surfaces due to dwelling of workpiece hi the moving MRP-fluid ribbon. To meet the finishing requirements of internal geometries and incorporating better inprocess control of finishing forces, a hybrid process from AFM and MRF, Magnetorheological Abrasive Flow Finishing (MRAFF) was developed hi the present invention. The hydraulically powered device of the invention is depicted in Figure 1. Since the process of the invention is novel, earlier experimental data is not available on its performance. Experiments were conducted to study the effect of magnetic field strength (B) on the surface finish and to have an insight into the finishing mechanism. Flat stainless steel workpieces of size 35x5x2 mm with supporting fixture were prepared. Initial center line average (CLA) surface roughness R« of approx. 0.5 - 0.6 um was obtained by grinding workpieces. Magnetorheological polishing fluid with 20 vol. % carbonyl iron powder (Grade CS from BASF, avg. particle size 18 um), 20 vol. % silicon carbide abrasive powder of 400 mesh size and 60 vol. % of viscoplastic base medium ( 20 wt. % APS grease and 80 wt. % paraffin liquid heavy) was prepared. The suspension was prepared by mixing abrasive and iron particles into continuous phase (grease + oil) and stirring with the help of specially designed multiple blade mixer. This results hi uniform dispersion of iron and abrasive particles hi the base medium. Magnetic field of around 0.574 Tesla (at 6A current) across the workpiece was produced with the help of C- shaped electromagnet, made of cold rolled annealed steel. Experiments were conducted at different magnetic field strengths. The surface scanning electron micrographs are shown in Fig. 2. After preliminary study, the finishing performance of MRAFF process is found to be mainly dependent on MRP-fluid composition for the same magnetic field strength, extrusion pressure and number of finishing cycles. MRP-fluid composition is one of the key parameters affecting final surface roughness in MRAFF process due to its role in fluid structure formation; hence it is taken up as a main factor for this study. In this study the effect of silicon carbide (SiC) abrasives and carbonyl iron particles (CIPs) size on decrease hi surface roughness value was investigated on stainless steel work pieces. A microscopic study of CIP chain structure formation was conducted. Based on this observation and suitable assumptions related to structure formation; final surface roughness was simulated and compared with the experimental results as discussed in the following sections. Finishing forces in MRAFF process are controlled by Theological properties of MRPfluid which comprises of carbonyl iron particles and very fine abrasives dispersed in viscoplastic base medium of mineral oil and grease. This composition exhibits unique reversible change in it* Theological properties on application and removal of external magnetic field. The magnetic field dependent yield stress and viscosity of MRP-fluid can be controlled by controlling magnetizing current in the electromagnet coils producing magnetic field across the finishing zone. The carbonyl iron particles acquire magnetic dipole moment proportional to magnetic field strength, and aggregate into chain like structure aligned in the field direction, embedding non-magnetic abrasive particles in between. Depending on the size and volume concentration of abrasives and carbonyl iron particles (CIPs), the bonding strength gained by abrasives through surrounding CIPs chains varies. To finish internal workpiece surfaces in MRAFF process, the MRP-fluid was extruded through the workpiece passage in the presence of magnetic field. Abrasion occurs selectively only where the change in rheological properties of MRP-fluid takes place from near Newtonian to Bingham plastic due to CIPs chain formation. Due to CIPs chain formation, non-magnetic abrasive particles get embedded between the chains, and gain bonding strength in proportion to magnetic field strength to perform finishing action. In this way the extent of abrasion of peaks by abrasives is controlled by magnetic field strength and the desired finishing characteristics are controlled by changing magnetizing current in the electromagnet. Finishing experiments were conducted on specially designed and developed hydraulically powered MRAFF setup. All experiments were conducted for 200 finishing cycles at 3.75 MPa hydraulic extrusion pressure and 0.531 Tesla magnetic flux density. The MRP-fluid was prepared with 20 vol. % carbonyl iron powder and 20 vol. % silicon carbide abrasives in 60 vol. % base medium of paraffin liquid and AP3 grease. The polishing fluid was prepared by mixing abrasive and iron particles into nearly continuous phase (grease + oil) and stirring with the help of specially designed multi-blade mixer. This results in uniform dispersion of iron and abrasive particles in the base medium. Magnetic field across the workpiece was produced with the help of C- shaped electromagnet, made of cold rolled annealed steel. Experiments were conducted on stainless steel ground workpieces (flat surfaces) with initial Ra value of ~0.30^m. Experiments were conducted using two different grades of carbonyl iron powders from BASF, CS and HS along with black silicon carbide of mesh size 800, 1200, and 2000. Before and after every experiment, the surface roughness profiles were recorded by Mahr Federal Surfanalyzer 5000. The surface roughness measurement results are summarized in Table 1. The highest improvement from 0.32 |j.m to 0.09 nm is observed in case of MRP-fluid containing CIP-CS and SiU-SUO and the least improvement is found in CIP-HS and SiC-2000 combination for There was not much improvement in surface roughness for Expt. Nos. 4-6 (Table-1) corresponding to CIPs of 3.5 urn diameter much smaller than SiC diameter, though small change in R» value was noticed. The changes in Ra value in these cases are very less. The obvious reason for this observation is that the chains formed from small carbonyl iron particles of HS grade (3.5um) are not strong enough to hold the bigger abrasive particles, and are unable to provide required finishing forces. This reasoning is supported in the following sections by theoretical analysis of chain structure formation and surface roughness profile simulation. The study of chain structure formation on application of magnetic field helped to understand the role of particle size on surface finish improvement. The structures of six different MRP-fluid compositions were investigated. To study the magnetic forces coming on abrasive particles during finishing operation, structural arrangement of carbonyl iron particles around abrasive particles are calculated theoretically considering their occupancy in a unit cube. It is known that the carbonyl iron particles acquire magnetic dipole moment in the presence of external magnetic field. When the dipolar interaction forces between particles exceed their thermal interactions, the particles aggregate into chains of dipoles aligned in the field direction. These chains form columnar structure at higher concentration of carbonyl iron particles. For simplifying theoretical simulation of chain structure, it is assumed that iron particles rearrange around SiC particles in the direction of magnetic field and repeat itself in complete volume spanning from one end to the other of the fixture between electromagnet poles. Due to the presence of non-magnetic abrasive particles in the MRP-fluid, the chains are rarely continuous; instead terminate at the abrasive particles if come in between chain path. Iron particles are assumed to be uniform in size and homogenously distributed spheres that can be magnetically modeled as identical induced dipole moments. The chain is formed by the alignment of spherical CIPs in the magnetic field, touching end to end diametrically. For non-magnetic silicon carbide abrasive particles, it is assumed that there is little movement of the particles hi MRP-fluid on the application of external magnetic field. They get trapped between the iron chains wherever they were before the application of magnetic field with slight adjustment. So, the numbers of silicon carbide particles hi unit area are calculated by considering their uniform distribution inside the MRP-fluid. On the basis of our assumptions, forces on abrasive particles used for finishing during MRAFF process are calculated considering similar arrangements of CIPs around SiC particles. Calculations were done to estimate number of particles per unit cell (volume depends on particle sizes) for particle sizes specified hi Table 1 and the results are summarized hi Table 2. A unit cell occupies the MRPfluid volume available around integer number of SiC particles. Depending on the volume concentration, the volume available around one SiC particle is calculated. Based on particle sizes, the number of CIP per SiC is calculated and then these numbers of iron particles are arranged around SiC based on the possible equilibrium positions and space available. required to calculate the forces on abrasive particles during finishing action. In MRAFF process, the spherical abrasive particle penetrates into the workpiece surface under the action of the normal magnetic force on carbonyl iron particles in the presence of external magnetic field. The abrasive grain produces a groove on the workpiece surface whose section corresponds to the profile of the penetrated portion of the grain. Under hydraulic pressure, when the penetrated abrasive grain is translated horizontally, the shearing of workpiece material hi front of abrasive grain takes place when shear force by the fluid (Fshear) on the projected area of the penetrating abrasive (above the portion embedded into the surface) is greater than the reaction force (Rshear) on the embedded projected area of the abrasive due to the strength of the workpiece material as shown in Fig. 3. Condition for shearing, Fshear > Rshear Where, A = total projected area of abrasive grain, A'— projected area of embedded portion of abrasive in workpiece surface, ay = yield stress of stainless steel workpiece in shear, and ry = fluid shear stress. On comparison after calculations using Eqs. (1) and (2), the Fshear is found to be greater than Rshear to perform finishing action. For finishing experiments two multilayered copper coils each with 2000 turns of 17 SWG were used to produce magnetic field in the gap of 30 mm (Fig. 4). To calculate normal force on any ferromagnetic particle (act as magnetic dipole) in the external magnetic field, variation of magnetic flux density (B) is calculated between the pole pieces. Using formula for magnetic flux density due to a finite solenoid, the value of B at any point, at a distance ' x' from coil 1 (Fig. 4), is the vector sum of BI, flux density due to coil 1 and 82, flux density due to coil 2. Where, TJ, r2 and/, are core radius, outer radius and length of electromagnet coil, respectively, x is the distance from pole face, //0 is magnetic permeability of free space, / is magnetizing current, and n is number of turns per unit length. The variation of flux density in the air gap due to electromagnet used was also experimentally measured using a Gauss meter, with cold rolled annealed iron core. The measurements were done from coil 1 to coil 2 in forward direction and then from coil 2 to coil 1, backward. Both readings were almost overlapping so average is taken and value of B is plotted along with theoretical variation hi Fig. 5. The relative permeability of iron core was found out by measuring B in presence and absence of iron core and was 7.26. Theoretical and experimental variation of B with distance x is plotted hi Fig. 5 for the values of x = 0 to x = 24 mm as per the coordinate axis shown hi Fig. 4. The theoretical variation of B hi the gap is quadratic, therefore after fitting the quadratic equation (dashed curve hi Fig. 4) to the experimentally obtained variation Force on a small ferromagnetic particle of mass m is given by, where, //0 is magnetic permeability of free space, zm is magnetic susceptibility of carbonyl iron particles (CIPs), m is mass of CIP, and H is Magnetic field strength. For practical purposes, it is advantageous to replace field strength with magnetic induction using relation B = n0H , so that Eq. (7) becomes ......... (8) Owing to the bigger size of flat pole piece hi comparison to the diameter of workpiece fixture, the variation of B hi y direction is negligible, hence after neglecting it the To calculate the force on abrasive particles due to magnetic force on carbonyl iron particles near workpiece surface, their structural arrangement and alignment are drawn as per possible equilibrium structure hi unit cell and are shown schematically hi Fig. 6. The Eq. (9) for calculating force involves the mass susceptibility^ of carbonyl iron particle. To calculate the mass susceptibility Xm of CS and HS grades, the M-H curves are plotted using "Parallel field vibrating sample magnetometer (VSM) model 150A". The forces for each experiment are calculated in the following paragraphs. From Table 2 it is found that there are -1.18 carbonyl iron particles per abrasive particle in unit cell volume which are in contact with the workpiece surface for experiment 1. Considering configuration of Fig.6 (a), the force on abrasive particle is calculated as follows: The possible arrangement of one CIP around one SiC in a cube of 25.46 urn edge is their arrangement along diagonal. Magnetic force Fm on CS grade carbonyl iron particle of diameter 18um at a distance 20.18 urn from work piece surface and at x = 3.02018 mm (3 mm fixture and workpiece thickness + perpendicular distance of CIP from work piece surface) is calculated fromEq. (6) as, £ = 0.557618 Tesla Differentiating Eq. (6) with respect to x and substituting value of x (0.003028) we get, — = -3.85028 dx The value of^mat B = 0.557618 Tesla obtained from M-H curve is %„ =3.985x10"4 m3/kg. Substituting these values in Eq. (9), we get Fm ~ 16.216x10'9 N. Following the above procedure, forces for five other experiments whose configurations are shown in Figs. 6b - 6f have been computed and the same are given in Table 3. (Table Removed) Where, Dp and L, are MRPF-cylinder piston diameter and stroke length respectively. Df is the fixture's inside diameter. The number of abrasive particles in an extrusion length of 459.201 mm is calculated from/,,/**, where 'a' is the edge of cube around each abrasive particle or linear spacing between center of two adjacent abrasive particles (Fig. 7). Numbers of abrasive particles passing over a roughness peak per stroke are calculated as number of abrasive particles in an extrusion length, Le/a. Initial surface roughness data input to the model was taken from the Surfanalyser 5000 instrument in the form of ordinates of all sampled points in the profile at equal interval. To update the surface profile after each stroke, depth of indentation by spherical abrasive on each peak is calculated from Eq. (1 1) (this equation can be derived from the AOAB in Fig. 3) and subtracted from the peak height as shown in Fig. 8. The indentation diameter Dt in Eq. (11) is calculated from Brinell hardness number given below, Where, Dg is the abrasive grain diameter in m, Dt is the indentation diameter in m, i normal indenting force on abrasive in N, and HBHN is the work piece Brinell hardness. The new peak height Y{ after one stroke with Ng active grains/stroke is given by, (14) If the point is not a peak point hi the data file (for example Ya and Ya in Fig. 8), then it is transferred to final profile as it is. To update the peak heights, new peak points were calculated after each stroke and updated profile data were passed for processing stroke. Before and after all strokes, the center-line-average surface roughness value (Ra) from profile data points was calculated using Eq. (15), Where, N is number of data points and Yt is roughness height at those points. To calculate final Ra value based on theoretical indentation values, software in 'C' programming language was written as per flow chart shown in Fig. 9. The theoretically obtained final Ra values after simulation are summarized in Table 4. The theoretically calculated Ra values are in close agreement with the experimental results with maximum error of 12% except for Expt. 1. For Expt. 2 and 5, the simulated and actual profile is shown hi Fig. 10 and 1 1 after 200 cycles. Comparatively large indentations are obtained theoretically when the abrasive particles and CDPs are of approximately same size (Expt. 1) as compared to the case when CIPs are smaller hi size compared to abrasive particles in Expt. 4-6. This conclusion closely resembles with the experimental observations. Thus it can be concluded that the theoretical modeling clearly captures the fact that CLP and abrasive particle size ratio plays an important role hi final roughness value Following assumptions are identified as the main reasons for the variation between the experimental and theoretical Ra values: i) The carbonyl iron chains and SiC structure are assumed to repeat and span from one end to another of the fixture. This assumption is made to simplify the physical model, though in actual case the chain like structures formed between magnetic poles are more complex as can be seen in Fig. la. Iron chains many times terminate at the abrasive particles that come in their way and form clusters by aggregating into cylindrical columns. ii) All abrasive particles are assumed spherical of average diameter, calculated from thenmesh size. In practice, no two abrasive particles resemble each other in shape and size. iii) The abrasive particles are assumed uniformly distributed in MRP-fluid. It is observed microscopically also that this assumption is not very much true in case of carbonyl iron particles which are smaller as compared to abrasive particles. The number of abrasive particles on the workpiece surface reduces significantly when mixed with smaller CIPs. iv) Though change in surface roughness values hi experiment number 4-6 with very fine CIPs was observed, but the surface roughness profile was not reflecting substantial change. /) The normal magnetic force on iron particle in a stationary system (no shearing applied) on the application of magnetic field shows steady increase with time after an initial jump. This normal force decreases with strain and reaches plateau value at large strains. In calculating normal indentation force this decrease is not considered and the normal force is assumed constant, which results in comparatively higher indentation. The effect of CIP and abrasive particle size in MRP-fluid composition on change in surface roughness is investigated hi the study. Theoretical justifications are derived through efforts to understand the physics involved during finishing action in MRAFF process. Following are the main conclusions made after experimental study and theoretical modeling: 1. The role of magnetic field strength in MRAFF process is clearly distinguished, as at zero field conditions no improvement hi surface finish is observed, and the improvement is significant at high magnetic field strength. This is because, in the absence of magnetic field the carbonyl iron particles and abrasive particles flow over the workpiece surface without any finishing action due to the absence of bonding strength of CIPs. As the magnetic field strength increased by increasing magnetizing current, carbonyl iron particles chains keep on holding abrasives more firmly and thereby result hi increased finishing action. Even magnetic flux density of 0.1521 Tesla is capable of removing to some extent, loosely held ploughed material left after grinding process and expose the actual grinding marks made by abrasives. i) For the same magnetic flux density, the finishing forces on abrasive particles are mainly dependent on the number of CIPs in their vicinity, their microstructural arrangement and size. The magnetic force on a carbonyl iron particle is a function of particle volume, volume susceptibility, and its position in the field. Owing to this, size of CIP in comparison with abrasive size is an important factor affecting final surface roughness in MRAFF process. Smaller size CIPs are incapable to provide necessary finishing forces for bigger abrasive particles, hence result in weak bonding strength. Due to these weak bonding forces there was negligible or very less improvement in surface finish. ii) For the same CIP size the surface finish improvement decreases with decrease in abrasive particles size due to decrease in indenting forces and distribution of forces on more abrasive particles. The above disclosure and accompanying drawings are illustrative of the invention and modifications and variations are possible without departing from the scope and spirit WE CLAIM; 1. An abrasive flow finishing device and a process of abrasive flow finishing comprising atleast a pair of hydraulic unit namely hydraulic cylinder, each of which is connected to MRP-fluid cylinder, an electromagnet coil disposed on either side of a workpiece fixture provided between the MRP-fluid cylinders wherein the cylinders are housed in a frame and the workpiece fixture is attached to a workpiece. 2. An abrasive flow finishing device as claimed in claim 1, comprising a hydraulic circuit. 3. An abrasive flow finishing device as claimed in claim 1 or 2, wherein the fixture is made of non-magnetic material to prevent magnetic field isolation inside the fixture. 4. An abrasive flow finishing device as claimed in claim 1, wherein the abrasive flow finishing process comprising steps of:- - fixing of a workpiece to a workpiece holder followed by attachment of fixture to the holder, - fixing of MRP-fluid between workpiece fixture and holder followed by fitting of the same on the top MRP-fluid cylinder with a gasket in between and bringing down top cylinder over the workpiece fixture so as to form a closed MRP-fluid link, - placement of electromagnet coils on either side of fixture with pole facing and touching workpiece holder producing north and south on the workpiece face, - adjustment of current in the coils, - filing of chilled water and ice into a constant temperature bath to cool electromagnet coils, - adjustment of hydraulic extrusion pressure on the variable delivery pump of hydraulic pack, - connection of thermocouple of temperature data logger with the workpiece holder followed by operation of hydraulic unit and hydraulic relay controller. 5. Abrasive flow finishing process as claimed in claim 4, wherein the flux density varies from 0 to 0.574 Tesla and the pressure varies from 0 to 5 Mpa. 6. An abrasive flow finishing device and a process as claimed in claim 1 8s 4, wherein magnetorheological polishing fluid comprising 5-30% of carbonyl from powder by volume, 5-30% of abrasive by volume and a base medium prepared from 40-90% of grease and mineral oil. 7. An abrasive flow finishing device and a process as claimed in claim 1 & 5, wherein the carbonyl Iron powder and abrasive are preferably 15-25% by volume. 8. An abrasive flow finishing device and a process as claimed in claim 6, wherein abrasive is selected from diamond, Boron carbide, Silicon carbide, Alumina and Chromium oxide.

Documents:

1991-del-2005-1991-del-2005-Abstract-(03-01-2013).pdf

1991-del-2005-1991-del-2005-Claims-(03-01-2013).pdf

1991-del-2005-1991-del-2005-Form-2-(03-01-2013).pdf

1991-del-2005-1991-del-2005-Form-5-(03-01-2013).pdf

1991-del-2005-abstract.pdf

1991-del-2005-claims.pdf

1991-del-2005-correspondence-others.pdf

1991-del-2005-description (complete).pdf

1991-del-2005-drawings.pdf

1991-del-2005-form-1.pdf

1991-del-2005-form-2.pdf

1991-del-2005-form-26.pdf

1991-del-2005-form-3.pdf

1991-del-2005-form-5.pdf

1991-del-2005-patition others.pdf

1991-DELNP-2005-Abstract-(05-09-2011).pdf

1991-DELNP-2005-Claims-(05-09-2011).pdf

1991-DELNP-2005-Correspondence Others-(05-09-2011).pdf

1991-DELNP-2005-Description (Complete)-(05-09-2011).pdf

1991-DELNP-2005-Form-1-(05-09-2011).pdf

1991-DELNP-2005-Form-2-(05-09-2011).pdf

1991-DELNP-2005-GPA-(05-09-2011).pdf