Wtc2005-64260 Wtc2005-64260

Home , Bingham plastic

Proceedings of WTC2005 ProceedingsWorld Tribology of WTC2005: Congress III September 12-16,World 2005, Tribology Washington, Congress D.C., USA III September 12-16, 2005, Washington, D.C., USA

WTC2005-64260 WTC2005-64260

EVALUATION OF RHEOLOGICAL PROPERTIES OF MAGNETORHEOLOGICAL POLISHING FLUID AND THEIR EFFECT ON SURFACE FINISH IN ULTRA PRECISION FINISHING PROCESSES

Sunil Jha V.K.Jain++ Mechanical Engineering Department, Indian Institute of Technology Kanpur - 208016 (India) ++ Corresponding Author; E-mail: [email protected]; Voice: +91-512-2597916; Fax: +91-512-2597408/2590007

ABSTRACT of finishing forces, a variant of the MRF and AFM processes, Magnetorheological finishing (MRF) process for automated MRAFF [8] was developed. lens finishing and Magnetorheological abrasive flow finishing The MRP-fluid comprises of carbonyl iron particles (CIPs) (MRAFF) for internal geometries rely on unique smart and very fine abrasives dispersed in a viscoplastic base medium behavior of MRP-fluid. The rheological properties of MRP- of mineral oil and grease. It exhibits reversible change in its fluid depend on carbonyl iron particle (CIP) and silicon carbide rheological properties on the application and removal of an (SiC) particle size, their volume concentration, magnetic external magnetic field. In the presence of a magnetic field, the properties and applied magnetic field strength. To study the CIPs acquire a magnetic dipole moment proportional to field effect of particle size on rheological properties of MRP-fluid, a strength and aggregate into a chain like structure aligned in the hydraulically driven specially designed capillary rheometer is field direction [9], embedding non-magnetic abrasives in fabricated. The best surface finish improvement was obtained between. Depending on the size and volume concentration of with MRP-fluid containing approximately equal diameter of abrasives and CIPs, the bonding strength gained by abrasives abrasive particles and CIPs. Least improvement was noticed through surrounding CIPs chains varies. The objective of the with smaller CIPs and bigger abrasive combinations used. This present work is to evaluate the rheological properties of MRP- is because the smaller size CIPs are incapable of providing the fluid with different particle size of its constituents and study necessary finishing forces for bigger abrasive particles, which their effect on change in surface roughness. results in weak bonding strength. Experimental Set-up: The finishing experiments were conducted on an MRAFF setup designed and developed by the INTRODUCTION authors [8]. The MRP-fluid is extruded through the workpiece The available traditional and advanced finishing processes passage to be finished utilizing two opposed cast iron cylinders alone are incapable or uneconomical for producing desired under the presence of an external magnetic field. The transition surface characteristics on internal geometries. Abrasive flow in rheological properties of MRP-fluid takes place in the machining (AFM) process [1] was developed to finish internal finishing zone immersed in a magnetic field produced by an complex geometries by allowing abrasive mixed polymeric electromagnet . medium to flow over the surface under pressure. The abrading Due to the high yield stress value, the presence of abrasive forces in the AFM process are a function of the viscosity of the particles and the requirement of a magnetic field, no viscoelastic polymeric base medium [2], which are difficult to commercially available rheometer was found suitable for the control during operation. Magnetic field assisted manufacturing measurement. Hence, a specially designed pressure driven processes are relatively new finishing processes and they are capillary rheometer is fabricated, which consists of MRP-fluid becoming popular in finishing, cleaning, deburring and reservoir, stainless steel capillary, hydraulic actuator, hydraulic burnishing of metal and advanced engineering material parts. system and electromagnet. This process can produce surface finish of the order of a few Experimentation: Finishing experiments with MRP-fluid nanometers [3-5]. prepared with two different grades of CIP (HS & CS) and three The in-process control of MRP-fluid viscosity and yield mesh sizes of SiC (800, 1200, & 2000) were conducted on shear stress using an external magnetic field adds determinism stainless steel workpieces. All experiments were conducted for to the processes in which it is used. One such process is MRF 200 finishing cycles at 3.75 MPa extrusion pressure and 0.53 [6] for lens finishing which works well for flat, spherical and Tesla magnetic flux density. Each MRP-fluid was prepared by aspherical surfaces [7]. To meet the finishing requirements of mixing 20 vol. % CIP and 20 vol. % SiC in 60 vol. % internal geometries and incorporating better in-process control viscoplastic base medium of paraffin liquid and AP3 grease

1 Copyright ©2005 by ASME using a specially designed multi-blade mixer. Magnetic field 20CS-20SiC800 and Fluid-2: MRPF-20HS-20SiC800 at 2000 across the workpiece was produced with the help of an Gauss. Similar curves were drawn for all fluid compositions. electromagnet. Before and after every experiment, the surface roughness profile was recorded. For evaluating rheological 80 properties, the capillary rheometer (Fig. 1) was used. The fluid 70 was forced through a fine capillary and the viscosity and yield 60 Fluid-2 shear stress were determined from the measured volumetric 50 flow rate, applied pressure and the capillary dimensions. 40 30 Fluid-1 20 Shear Rate (1/s) Rate Shear Hydraulic 10 Actuator 0 4 6 8 10121416182022 MS Plate Wall Shear Stress (kPa) Piston Rheometer MRP fluid Plate Fig. 2: Flow curves of MRP-fluids with CS (Fluid-1) and HS Reservoir 3-φ A.C. Motor (Fluid-2) CIPs and 800 mesh SiC at 2000 Gauss.

Electromagnet Supporting P CONCLUSIONS bar All fluid compositions exhibit near Bingham Plastic behavior up to a critical wall shear stress. MRP-fluids with HS (3.5 µm Stainless Steel Hydraulic diameter) grade CIP sheared at a faster rate after a critical wall Capillary Fluid Unit shear stress or an external pressure at which complete breakage Collector of CIPs chain structure takes place. This has a great impact on finishing action and plays an important role in selecting Fig. 1: Pressure driven capillary rheometer extrusion pressure.

ACKNOWLEDGMENTS RESULTS AND DISCUSSION The financial support of CSIR Project No. The surface roughness results are summarized in Table 1. 22/0369/04/EMR-II, Govt. of India, is kindly acknowledged.

Table 1: Magnetorheological Abrasive Flow Finishing results REFERENCES Ex CIP SiC Initial Final ∆Ra % 1. Rhodes L. J., Abrasive flow machining: a case study, pt. Dia. Dia. Ra Ra ∆Ra Journal of Material Processing Technology 28 (1991) 107- (µm) (µm) (µm) (µm) 116. 1. 18 (CS) 19 0.32 0.09 0.23 71.87 2. Williams R.E., Rajurkar K.P., Rhodes L.J., Performance 2. 18 12.67 0.28 0.17 0.11 39.28 characteristics of abrasive flow machining, SME technical 3. 18 7.5 0.31 0.23 0.08 25.80 paper FC89-806 (1989). 4. 3.5 (HS) 19 0.34 0.30 0.04 11.76 3. Shinmura T, Takajava K, Hatano E., Study on Magnetic 5. 3.5 12.67 0.28 0.24 0.04 14.28 Abrasive Process – Application to Plane Finishing, Bull. 6. 3.5 7.5 0.21 0.20 0.01 4.76 Japan Soc. of Precision Engg., 1985 19 (4) 289-291. 4. M.Fox, K.Agarwal, T. Shinmura, and R.Komanduri, The highest improvement in surface finish from 0.32 µm to Magnetic Abrasive Finishing of Rollers, Annals of CIRP, 0.09 µm was observed in the case of MRP-fluid containing 1994, 43 (1) 181-184. CIP-CS and SiC 800 mesh, and a subsequent decrease was 5. Yamaguchi H., and Shinmura T., Study of the surface observed with finer abrasive combinations. With very small modification resulting from an internal magnetic abrasive size CIPs of HS grade, the surface finish improvement was finishing process, Wear 1999, (225-229), 246-255. small or negligible with all combinations of abrasive sizes. The 6. Kordonski W. I., Jacobs S.D., Magnetorheological reason for this is that the chains formed by small CIPs of HS finishing, Int. Journal of Modern Physics B 10 (23, 24) grade (3.5 µm) at the given flux density are not strong enough (1996) 2837-2848. to hold the bigger abrasive particles, and they were incapable of 7. Kordonski W, Golini D, Progress update in providing the required finishing force. A justifiable reasoning Magnetorheological finishing, Int. Journal of Modern was developed after observing the CIPs chain formation under Physics B 13 (14,15&16) (1999) 2205-2212. an optical microscope and calculating theoretically the forces 8. Jha Sunil, Jain V. K., Design and development of on the abrasive particles. Appropriate assumptions were made Magnetorheological abrasive flow finishing (MRAFF) to simplify the chain structure simulation. process, International Journal of Machine Tool and Volumetric flow rates were obtained over a range of Manufacture 44/10 (2004) 1019-1029. pressures (3.0 MPa – 4.0 MPa in steps of 0.25) for each fluid 9. Furst E.M, Gast A.P, Micromechanics of composition. Plots were then constructed between rate of shear Magnetorheological Suspensions, Physical Review E 61 and wall shear stress. Fig. 2 shows curves for Fluid-1: MRPF- (6) (2000) 6732-6739.