A STUDY OF VISCOELASTIC MAGNETIC ABRASIVE FINISHING PROCESS

Abstract

Magnetic field Assisted surface finishing concept started during 1940s in the USA, subsequently different countries started working in this field and developed processes like Magnetic Abrasive finishing, Magnetic flow finishing, Magnetorheological finishing process, Magnetorheological abrasive flow finishing process. Dr.W.Li[2013] developed Viscoelastic Magnetic Abrasive finishing process. In the present thesis Entitled “A Study of Viscoelastic Magnetic Abrasive Finishing Process” an investigation has been made about the finishing of Complex Internal surfaces and external surfaces. First two chapters are Introduction and the Literature review. In the third chapter, Viscoelastic Magnetic Abrasive medium has been prepared with Silicone oil, Transformer oil and AP3 Grease. These Media have been tested for their Viscosity by Rheometer. Based on the results obtained, Viscoelastic Medium to be used for internal finishing of the Spline shaft and external plane surfaces has been decided. In the fourth chapter different Optimisation techniques presently adopted has been briefly discussed. In the Fifth Chapter, Modelling and Simulation of the Permanent magnets with same material, same volume and different geometries has been done. Based on the results obtained, it has been observed that Fan Magnet and Arc Magnet are found to give better Magnetic flux density for the same working gap. A segmental arc Magnet, normally used for Power generation by Wind turbine has been used for creating Magnetic flux density for finishing of the internal surface of the Spline shaft. Magnetic Flux density of the spline shaft for three different levels has been simulated. Based on the simulated results, the median value has been taken as the Magnetic flux density for finishing operation. Abrasive Flow Machine in the Advanced Manufacturing lab is used for finishing of the internal splines. An Aluminium fixture has been designed and XXII fabricated for accommodating the Segmental Magnet, which encompasses the spline shaft. The rotary motion is provided to the spline shaft with set of gears and the Viscoelastic Magnetic Abrasive medium gets reciprocating motion due to the controlling motion. Medium makes motion inside the spline shaft due to the difference of pressure. Six process parameters have been considered and experiments have been performed based on the L27 Orthogonal array of Design of experiments of Taguchi. Nine specimen have been prepared and have been subjected to Finishing process based on Design of experiments. In first cycle Magnetic flux density of Level 1 is considered and all the nine specimen have been finished under this flux density. In second cycle these nine specimen have been subjected to finishing operation based on the Magnetic flux density Level 2. The last cycle of finishing has been performed with Magnetic Flux densities of Level-3. After every cycle each specimen is thoroughly cleaned and greasiness has been removed. Surface roughness and the mass of the specimen before and after each cycle for all the nine specimens has been measured. Optimisation for the maximum material removal has been done with Taguchi’s Linear regression model using MiniTab 17 software. Results have been critically examined. In the Seventh chapter, finishing of Brass, Steel and Aluminium Specimens has been carried out. Test rig for this is the CNC Drilling and Tapping Machine centre available in Metal cutting lab of Delhi technological university. A mild steel based Magnetic finishing tool has been designed and fabricated, which accommodates the N52 cylindrical permanent magnet. Magnetic tool that has been fixed to the spindle of the test rig rotates and the Viscoelastic Magnetic abrasive medium attached to the powerful magnet finishes the top surface of the specimen during the rotary motion and feed motion of the spindle. In total six process parameters have been considered for external finishing of the specimen made of all the three material. Experiments have been performed based on Taguchi’s L27 Orthogonal Array of Design. Only Nine specimen have been considered for finishing operation XXIII and each specimen is subjected to three cycles. First cycle of experiments for all the nine specimens is based on 2 mm working gap, second cycle with 1.5 mm gap and the third cycle is with 1 mm gap. After every cycle the specimen have been thoroughly cleaned and greasiness has been removed. Surface roughness, Mass of the specimen before and after each cycle has been noted and tabulated. Optimisation has been done for Maximum metal removal by Taguchi’s linear regression model using Minitab 17. Results have been critically examined. Residual stresses of each specimen before the start of the first cycle has been measured and the values of the residual stresses has been measured after finishing the third cycle and comparison shows that the specimens are subjected to compressive stresses. Sliding wear test has been performed on the specimen finished with VEMAF process. Specimen with best surface finish have been selected from all the three materials and cut into size as per the requirement. Eighteen Cylindrical specimens each for Brass, Al6351T6 and Mild steel have been prepared, which are having surface roughness value of the order 0.09 μm ±10%. Three process parameters; Load, Time and Frequency have been considered for wear test. L9 Orthogonal Array of design of Taguchi has been selected for performing the wear test. Rough surfaces are the rear surface of the finished surfaces and these rough surfaces have been subjected to Wear test. The initial and final masses have been noted for the specimen, the difference of which gives the wear for the rough side of the specimen. After completing the wear test on all the rough surfaces, same procedure is adopted for the finished surfaces also. The same procedure has been adopted for all the three materials. Results have been analysed and Optimisation has been done with Minitab 17 based on Taguchi’s linear regression model. Significance of process parameters, their ranking has been tabulated.