Experimental Investigations of Magnetorheological Honing Process for Improved Finishing Of Ferro-Magnetic Materials

Abstract

The various ferromagnetic cylindrical components such as injection barrel, cylindrical mold and die, hydraulic cylinders etc. are now-a-days of being a greater demand in the manufacturing industry. Today, these components are mainly finished by the traditional finishing processes namely; grinding and honing. During the finishing processes, the uncontrollable finishing forces provided by the rigid abrasive stones on the internal surface of the cylindrical workpiece which may result in various surface defects such as deeper grooves, cavities, grooves with sharper edges and ploughed materials. Such defects decrease the efficiency as well as the reliability of the cylindrical components during its actual functional applications in industries. The requirement of the highly finished surface (i.e. defect-free surface) is still important challenged in today’s industry for producing a precise finish surface. The better surface characteristics requirement on these components can lead to the closer tolerance design, better surface geometry, and longer service life etc. Also, the functional capability of a surface mainly depends on the load - bearing capacity, wear and friction resistance, and fatigue strength etc. which mainly controlled by reducing the surface roughness values. The existing developed magnetorheological (MR) fluid based finishing processes such as magnetorheological abrasive flow finishing (MRAFF) and rotational-magnetorheological abrasive flow finishing (R-MRAFF) are found more suitable for precise finishing of the internal surface of the non-ferromagnetic cylindrical workpieces made with materials such as stainless steel, brass etc. But, due to its design structure, it is likely less effective in finishing of the internal surface of ferromagnetic cylindrical workpieces. The reason is that the electromagnet is located outside the cylindrical workpiece and MR polishing fluid inside the cylindrical workpiece. Therefore, the higher magnetic flux density gradient is obtained on the internal ferromagnetic cylindrical surface than the MR polishing fluid. This result in MR polishing fluid gets stuck on the internal surface of the ferromagnetic cylindrical workpiece. Thus, there is no relative motion can be possible between the MR polishing fluid and the internal surface of the ferromagnetic cylindrical workpiece during the finishing operation. These processes are found most suitable for significant finishing of the internal surface of the non-ferromagnetic cylindrical workpiece than the ferromagnetic cylindrical workpiece. In present research work, to overcome these challenges, a new MR honing process is developed for precise finishing of the internal surface of the ferromagnetic cylindrical workpiece. The finishing tool has been designed along with electromagnet and made to move together inside the cylindrical ferromagnetic workpiece surface and finished the internal surface by its rotational as well as reciprocation movement like the honing tool movement with controlled magnetic field. The newly designed finishing tool provided a uniform level of finishing as its entire outer finishing surface obtained a uniform magnetic flux density which is more useful to provide better in closer tolerance design, higher bearing load capacity and longer service life in various cylindrical machine components. This new tool design has ensured the higher magnetic flux density gradient at outer finishing tool core surface than the internal surface of ferromagnetic cylindrical workpiece. As a result, the MR polishing fluid always retained on the outer finishing tool core surface and the required relative motion can be possible between the internal surface of the ferromagnetic cylindrical workpiece and the MR polishing fluid during the actual finishing operation. This is an important need to get finishing on the internal surface of the ferromagnetic cylindrical workpiece. The developed process can be found effective in enhancement of surface characteristics (i.e. by removing the various surface defects) of traditionally finished internal surfaces of ferromagnetic cylindrical workpieces. In present work, the MR honing tools (i.e. I-shaped core type and rectangular shaped core type) have been designed to ensure the maximum magnetic flux density always to be obtained on the outer finishing tool core surface as compared to the ferromagnetic cylindrical workpiece surface. To validate this present proposed design, the magnetostatic finite element analysis (FEA) has been carried out by using Maxwell Ansoft V13 (student version) software on the newly designed finishing tools. The finishing tool with rectangular shaped core has been found more suitable for providing a uniform level of finishing than the tool with I-shaped core as its entire outer finishing surface obtained a uniform magnetic flux density. The different MR polishing fluids are synthesized indigenously and these have been used for different experimentation in the present research work. The rheological behavior in terms of flow stability of synthesized MR polishing fluid has been carried out with the help of magnetorheometer with shear mode. To further check the feasibility of the present developed process, the preliminary experiments have been conducted to evaluate the finishing performance of developed MR honing setup with the designed MR honing tools for finishing of the internal surface of mild steel cylindrical workpiece. The percentage reduction in surface roughness (Ra) values with I-shaped tool core is found as 65-78% after 150 minutes of finishing. But, in case of MR honing tool with rectangular shaped tool core, it is found as 78-81% after 90 minutes of finishing. The results clearly revealed that the present finishing tool with the rectangular shaped core is found more suitable for significant finishing of the internal surface of the mild steel cylindrical workpiece than the I-shaped core tool. This is because the finishing tool with rectangular shaped core provided a uniform and efficient finishing, as its entire outer surface obtained a uniform magnetic flux density. This is more useful to provide close tolerance design, higher bearing load capacity and longer service life in various cylindrical machine components. The detailed studies of the statistical design (plan of experiments) are also conducted for internal surface finishing of EN-24 steel cylindrical workpiece. The EN-24 steel is commonly used in injection barrel. The response surface methodology using “Design expert 10” software has been used to plan and analyze the effect of different process parameters on the percentage change in surface roughness (Ra) value. The analysis of experimental data showed that the percentage change in surface roughness (Ra) value is more contributed by magnetizing currents followed by tool linear speeds, mesh sizes of carbonyl iron particles, tool rotational speeds and mesh sizes of SiC abrasive particles. Based on the results of response surface model after regression analysis, the optimum process parameters are found as 800 mesh sizes of SiC abrasive particles, 400 mesh sizes of carbonyl iron particles (CIPs), magnetizing current of 1.2 A, tool rotational speed of 500 rpm and tool linear speed of 50 cm/min. Using these optimum process parameters, the change in surface roughness (Ra) value is found as 96 nm from 401 nm after 90 minutes of finishing. The experimentation based on some industrial applications are also conducted for finishing the internal surface of ferromagnetic cylindrical materials such as gray cast iron used in the cylinder liner. The hardened EN-24 steel is used in the injection barrel of the molding machine. The improvement in surface characteristics of the internal ferromagnetic cylindrical surface clearly demonstrated the effectiveness of the present developed process. The present developed process is found effective for removing the various surface defects such as deeper grooves, honing grooves with sharper edges, torn and folded metals, cavities or holes and axial scratches from the traditionally cylindrical finished surface. These results may further lead to the enhancement of functional applications and longer service life of the components. Also, in this research work, the internal lateral and internal bottom surfaces of cylindrical ferromagnetic blind-hole type workpiece have been finished by using the two different MR finishing tools. The blind-hole type workpiece surfaces are mostly finished by the internal grinding (jig grinding) operations. After grinding, the surface defects such as the deep-seated groove, cavity, axial scratch, ploughed material etc. are generally induced on the blind-hole type workpiece surfaces. To further improve the surface characteristics, the experiments have been carried out on hardened EN-31 blind-hole type workpiece with the help of two MR finishing tools. The hardened EN-31 steel is commonly used in blind-hole type mold cavities. The results clearly revealed that the significant improvement in surface characteristics with almost negligible surface defects is found on final finished surfaces of blind-hole type ferromagnetic cylindrical workpiece as compared to its initial ground surfaces.