Design and Development of A Rotating Core Based Magnetorheological Finishing Process for Different External Cylindrical Surfaces

Abstract

The external surface finishing of cylindrical components at the nano-meter level with good surface characteristics is highly demanded in today’s industries for improving their operative functionalities. In industries, mostly traditional finishing process like grinding is used to finish the external surface of the various cylindrical components because of their easy accessibility and low making cost. Grinding makes use of a rigid bonded abrasive wheel. This rigid bonded abrasive wheel gives non-controllable finishing forces over the external surface of the cylindrical workpiece. Owing to this, sometimes the defects get produced like heat affected zone, micro-cracks, microstructural changes, folded metals, etc. on the final finished surface. Control over finishing forces is of great concern for achieving productive and defect-free components. Therefore, there is a mandatory requirement of the advanced finishing processes with controlled forces to finish the external surface of the cylindrical components for enhancing their operational life in real time applications. The finished surface using the advanced finishing processes has several benefits like close tolerance design, reduction in wear, friction losses and increase in product service life, etc. From the literature review, it has been found that very less work is done in fine finishing of the external cylindrical surfaces with the advanced finishing processes. Magnetic abrasive finishing (MAF) is the process that has been used to finish the cylindrical external surfaces. But MAF is used more effectively only to finish the hard material cylindrical surfaces. MAF process makes use of mostly a mixture of magnetic iron and abrasive particles as the magnetic abrasive brush. This may generate a lack of flowability and friction on the surface of ductile workpieces. As compared to the magnetic abrasive finishing, the magnetorheological (MR) finishing process has been found more flexible with its finishing medium as MR polishing fluid. In the MR finishing process, the carrier fluid facilitates more flexibility to move the active abrasives on the different shapes of the different workpiece materials. The flexibility and controllability of the MR polishing fluid make the process more effective for finishing the hard as well as soft material workpieces. The performance in the MR finishing processes majorly depends upon the relative motion between the stiffened MR polishing fluid and workpiece surface which is provided either by the motion of the workpiece surface or the tool. Recently, a turning type magnetorheological finishing process with the stationary magnetic curved tool tip surface was developed to finish the external surface of the cylindrical workpieces. In this process, the standard lathe machine is utilized to provide the rotational motion of the cylindrical workpiece against the stationary curved tool core tip surface. As the magnetized curved tool core tip surface was kept stationary, the active abrasive particles of the MR polishing fluid which perform finishing on the external surface of the rotating cylindrical workpiece may get less relative motion. Therefore, to improve the further process performance with an increase in relative motion, a rotating core-based magnetorheological finishing process has been developed in the present work where the magnetic tool core tip surface also gets rotational motion over the rotating external surface of the cylindrical workpiece. Also, the automatic feed arrangement is provided to the magnetic tool for finishing the external cylindrical workpiece longitudinally. The iron particles (IPs) chains are rotated along with the rotation of the tool core. This results in an increase in kinetic energy of the gripped active abrasive particles with the IPs chains which causes a better finishing performance. Finishing is performed on the external surface of the cylindrical workpieces by both the processes and their corresponding results are compared. The overall results revealed that the present developed process using a rotating flat tool core tip surface is more useful in finishing of external cylindrical surfaces as compared to the stationary curved tool core tip surface. Fine finishing of the tapered cylindrical components is the utmost need of the advanced manufacturing industries. The tapered coloured glass making industries require highly finished punches and cavity. To achieve this requirement, the developed magnetorheological (MR) finishing process with the rotating circular flat tip surface is utilized through its advancement for enhancing the surface characteristics of the tapered cylindrical workpiece. Also, the variation in linear velocity, helix angle, and the helical path made by the active abrasives on the tapered cylindrical surface has been analyzed in estimating the time taken for uniform finishing on the tapered cylindrical surface. The surface roughness parameters (Ra, Rq, and Rz) values get reduced to 97.28%, 95.82%, and 95.42% in 120 minutes of MR finishing with optimized parametric conditions. The surface waviness value gets reduced from the initial value of 0.841 μm to the final value of 0.205 μm. After the development of a rotating core-based MR finishing process, the best-required shape of the tool core tip surface in the magnetorheological finishing process is designed for improving the efficiency of the process on external cylindrical surfaces. The design of a rectangular shaped tool core tip surface is found more effective for uniform and higher flux density. The preliminary experiments are conducted on the cylindrical external surface using the rectangular shaped tool core tip surface and the circular-shaped tool core tip surface. After the magnetorheological finishing with the rectangular and circular shaped tool core tip surfaces, the final surface roughness values of the external surface of the cylindrical workpieces get reduced to 18 nm with the rectangular-shaped tool core tip surface and 45 nm with the circular-shaped tool core tip surface from the initial value of 310 nm in 60 minutes. Hence, the rectangular-shaped design of the tool core tip surface is found more useful to improve the efficiency of the present process. Further to achieve the fine finishing of the real-time industrial applications such as cold rolling rolls, micro-punches, winding grooved drum, spline shaft, and copper cylindrical rollers, the improved magnetorheological (MR) finishing process with the rotary rectangular tool core tip surface is employed. Cold rolling is one of the most vital manufacturing operations in the sheet metal industries. In cold rolling operation, the rolls are the most important component. If the surface of the rolls gets fine finished at a greater level, a smooth surface on the final products can be achieved. For effectively performing the MR finishing operation, the optimum process parameters are predicted by using the response surface methodology. The surface roughness gets reduced to 18 nm from the initial ground roughness value of 200 nm with the optimized parameters. After the MR finishing operation, the cold rolling rolls are tested their functional performance in the industry. The performance of the MR finished rolls surface is investigated and found better as compared with the ground rolls surface. The modern trend towards miniaturization has provided an innovative push towards the creation of micro-fabrication parts. Micro-extrusion is one such emerging process. Micro-punches are the main part of the micro-extrusion process. In the extrusion process, high contact forces are generated due to the sliding between the punch and billet. These high contact forces are governed by the surface topography of the punch. When the punches are finely finished, lesser contact forces are generated. On the basis of the applications, four industrial micro-punches are used in the present MR finishing investigation. After MR finishing, surface roughness values of the micro-punches of the initial ground surface 210, 230, 250, and 200 nm are reduced to 20, 20, 30, and 10 nm. Further, the fine level finishing of grooved drum surfaces is an essential requirement for enhancing the performance of the winding machines in today’s textile industries. The fine level of surface finishing is required as less as possible on the grooved surface of the textile winding drum. With the least possible roughness value over the external grooved surface of the winding drum, the breakage of the yarn and hairiness of the yarn can be reduced. After the 60 minutes of MR finishing, the average surface roughness value of the grooved drum surface gets reduced from 200 nm to 10 nm. The functional performance of the MR finished grooved drum is found better than the ground grooved winding drum due to the fine level of finishing. Also, fine and uniform finished spline shaft teeth surface tend to enhance the pressure distribution uniformly over the teeth surface and increase the life span of the spline shaft. Uniformly and fine finished teeth surface requirement has been accomplished by using the presently developed rotary rectangular tool core-based magnetorheological (MR) finishing process. The surface response methodology is utilized to optimize the process parameters for better finishing of the spline shaft. The Ra value gets decreased to 20 nm from the initial value of 270 nm with the optimum process parameters. The significant decrease in Ra value also improves the mechanical property as micro-hardness gets increased from 649 HV to 746 HV after the MR finishing of the teeth surface of the spline shaft. As in the printing industries, the copper cylindrical rollers play an important role in the printing operation. In the printing, the copper rollers are required fine and uniform finishing to uniformly distribute the colours and ingot material. Also, it provides the uniform distribution of the pressure. Fine and uniform finishing of copper cylindrical rollers are difficult due to its ductility and less hardness during the traditional finishing. Therefore, obtain fine finishing, initially, the MR polishing composition (%age concentration of electrolyte iron particles and aluminium oxide abrasives with base fluid) is analyzed for better performance. Furthermore, the central composite design is used to optimize the finishing parameters. The surface roughness value is reduced from the initial value of 190 nm to 25 nm after 60 minutes of MR finishing on 30 mm length and 25 mm diameter of the copper cylindrical roller. Finally, in the present work, a theoretical model is developed to predict the reduction in the surface asperities during the magnetorheological finishing of the external cylindrical surfaces. The rotational speed of the rectangular tool core on the rotating cylindrical work-part enhances the relative speed of active abrasives which decreases the pitch, helix angle, and increases the helical path length. This result enhances the uniform precise finishing on the cylindrical work-parts and also enhances the process performance. The %age error between the experimentally obtained Ra value and theoretical Ra value is found to be -2.08% to 4.76%, which is good agreement between the theoretical model and experimental results.