Investigations of a Rotational Magnetorheological Honing Process for Improved Productivity of Nano-finished Internal Surface of Cylindrical Workpieces

Abstract

Fine finishing of the internal surface of cylindrical components such as cylindrical molds and dies, hydraulic cylinders, power steering housing cylinders, industrial choke valves, cylindrical barrels for injection moulding, etc. is highly required to improve their operational functionality. The fine finished internal surface of cylindrical components also results in resistance to wear, corrosion, pitting, oxidation, and chemical damage. In industries, mostly traditional finishing processes like grinding or honing are used to finish the internal surface of the various cylindrical components because of their easy accessibility and low making cost. The traditional internal finishing processes use rigid hard bonded abrasives for finishing the internal surface of the cylindrical workpieces. The uncontrolled finishing forces applied by these hard bonded abrasives introduce various types of defects on the final finished surface such as residual stress, torn and folded metals, less surface finish, surface irregularities, micro-cracks, heat affected zone, reduction of strength, and reliability of the part, etc. Moreover, the traditional finishing processes can finish the surface upto a certain level because of the use of the rigid hard bonded abrasives tool and further to achieve a fine level of surface finishing without surface defects may not be possible. Therefore, there is a mandatory requirement of the advanced finishing processes to finish the internal surface of the cylindrical components after the traditional finishing processes for enhancing their operational life in various machines or systems. 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. To achieve efficient and defect-free finished internal surface of the cylindrical workpieces, recently a permanent magnet-based magnetorheological honing (MRH) process developed for finishing the internal surface of the cylindrical workpieces after various consecutive development in internal finishing techniques. This process is found advantageous for finishing the ferromagnetic as well as non-ferromagnetic variable diametric cylindrical workpieces. Also, this process finishes upto a nano-scale level of surface asperity with controlled finishing forces and without inducing any heating problem. The MRH tool was made rotating and reciprocating during the inside surface finishing of the stationary cylindrical workpieces. Further, with the resumption of all good qualities of the recently developed a permanent magnet-based MRH process and based on literature related to enhancement in relative speed of abrasive particles, a novel rotational magnetorheological honing (R-MRH) process has been developed in the present work for improved productivity and performance. In this process, the workpiece cylinder is also made rotating in the opposite direction at the same time when the tool is made rotating and reciprocating for finishing the inside surface of the cylindrical workpieces. Due to the oppositely rotating workpiece cylinder, the relative motion of the active abrasive particles gets enhanced which results in improved finishing productivity and performance. For developing this process, first of all, the theoretical analysis has been performed. Through the theoretical analysis, the effect of the rotating motion of the workpiece cylinder on the motion of the active abrasive particles has been studied in-depth. Also, under theoretical study, a surface roughness model has been developed to predict the finishing with the given process parameters. From the theoretical study, it is found that considering the tool rotational of 400 rpm, tool reciprocation speed of 70 cm/min, and cylinder workpiece rotation of 40 rpm opposite to the tool rotation in the present proposed R-MRH process, theoretically 65 nm of final surface roughness is evaluated with 40 min of finishing time from the initial surface roughness of 330 nm. Whereas in the existing MRH process when the tool rotation and reciprocation speed are kept the same i.e., 400 rpm and 70 rpm respectively but the workpiece cylinder is kept stationary, the final surface roughness is calculated as 102 nm with 60 min of finishing time from the initial surface roughness of 330 nm. Hence, theoretically, the improvement in productivity due to the workpiece rotation in the existing MRH process is clearly observed. Further, based on the result observed from the theoretical analysis, the present rotational magnetorheological honing (R-MRH) process is developed. The design requirement in developing the R-MRH process is to rotate the workpiece cylinder precisely in the same axis of rotation as the MRH tool rotates and reciprocates during the finishing operation. Therefore, to fulfil this need of the design requirement, suitable fixtures have been designed and fabricated for holding and rotating the different size of workpiece cylinders. Further, to confirm the improvement achieved in finishing performance and productivity as compared to the existing MRH process, an experimental study has been performed. From the experimental study, it is found that using the R-MRH process, the final surface roughness value of 50 nm is achieved in 40 min as compared to the 90 nm in 60 min which is achieved while using the existing permanent magnet-based MRH process for the same initial surface roughness value of 330 nm. This also further experimentally validates the significant improvement in finishing performance and productivity with the present R-MRH process. Furthermore, to validate the present developed R-MRH process performance in fine finishing of the real time industrial cylindrical workpieces, the detailed experimentations have been performed and successfully demonstrated on the inner surface of the outer race of ball bearing of EN-31 steel, cylindrical barrel of hydraulic cylinder, cylindrical mold for manufacturing the plastic bottle caps, and cast-iron cylindrical mold. So, the optimal parameters are predicted using the response surface methodology to achieve the maximum finishing performance in terms of percentage reduction in surface roughness value on the ferromagnetic EN-31 steel material and on the above-mentioned real time industrial cylindrical workpieces. The results obtained from the different experimentations performed in the present work have been analyzed through the surface roughness measurements, scanning electron microscopy images, waviness, and circularity of the inside cylindrical profile of the workpieces. From the results obtained in this work, it has been observed that the present developed R-MRH process is found in good order for finishing the internal cylindrical surface of the various industrial components with improved productivity for improving their operational functionality. Also, the fine finished internal surface of the cylindrical molds can produce end products with a smooth surface and geometrically correct. The R-MRH process is further improved in terms of the less expansive, less time, and labour-intensive by introducing an in-situ MR honing tool. Using the in-situ MR honing tool, the traditional honing as well as the R-MRH process can be performed on the internal surface of a cylindrical workpiece at a single setup. To confirm the feasibility of the in-situ honing tool for finishing the internal surface of the cylindrical workpiece through traditional honing as well as MR honing, preliminary experimentations have been performed. Using this tool, the internal cylindrical surface of the mild-steel workpiece has been finished first with the traditional honing and then the MR honing using the same in-situ tool on the same setup. The surface roughness value is achieved to 550 nm from the initial machined surface roughness value of 1510 nm with the traditional honing in 40 min and then 60 nm from the traditionally honed surface of roughness value of 550 nm with the present magnetorheological (MR) honing in 60 min. Hence, this result has experimentally demonstrated the ability of the newly designed in-situ MR honing tool to perform traditional honing as well as magnetorheological honing on a single setup which makes this tool more useful in industries for micro-finishing to fine finishing without changing the tool and finishing setup.