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Hybrid Chemo-Magnetorheological Finishing(HC-MRF) process is an advanced surface finishing process that utilizes the interaction of Magnetorheological Finishing and chemical etching to reduce the surface roughness of the cemented carbide cutting tools. Herein, Murakami’s reagent is used as a Magnetorheological (MR) fluid carrier medium to trigger chemical etching and mechanical abrasion. The synergic action reduces surface finishing time and increases process efficiency. However, optimizing process parameters during the HC-MRF process is required to improve process efficiency further. Response Surface Methodology(RSM) is used to develop the regression model to study the impact of process parameters (i.e. spindle speed, feed rate, and vol.% of Murakami’s reagent in MR fluid) on the surface quality. Three surface roughness parameters, namely average surface roughness (Ra), skewness (Rsk), and kurtosis (Rk), are opted to analyze the surface characteristics of the polished surface. Furthermore, optimization is performed with the help of a Genetic Algorithm(GA) to achieve the best surface quality following input parameters. The surface roughness (Ra) is reduced by 88.97% as the initial Ravalue decreases to 34.50 nm from 312.87 nm after the HC-MRFprocess. The results obtained from RSMand GAare in good agreement with the experimental results. The optimum value of feed rate, spindle speed, and vol.% of Murakami’s reagent in the MR fluid while achieving minimum surface roughness value (i.e. 31.26 nm) through GA are 1.2 mm/min, 23 rpm, and 53%, respectively. The measured kurtosis (Rku) value of 0.64 at the optimum process parameter condition represents flat peaks on the surface roughness irregularities of the polished surface. Similarly, a skewness (Rsk) value of 1.46 signifies that the number of peaks is higher than the number of valleys on the polished surface. Furthermore, it is observed that the Vol.% of Murakami’s reagent in MR fluid is the most significant process parameter compared with other parameters among all responses.

Surface roughness improvement of the freeform surfaces is essential for the enhanced functionality of the components, including implants, turbine blades, microchannels, etc. The exclusion of human involvement during the finishing of freeform surfaces prevents hazardous exposure to particulate and provides uniform surface quality. Different surface finishing techniques, including vibratory finishing, Abrasive Flow Finishing(AFF), Electron Beam(EB) Irradiation, Electrolytic in-process Dressing(ELID) grinding, etc., have been developed to automate the finishing operation. However, some limitations are associated with the preexisting techniques, e.g., the process controllability of AFF and vibratory finishing, recast layer formation during EB irradiation, and low productivity of ELID grinding. Hence, a novel method for surface improvement, namely, Hybrid Chemo-Magnetorheological Finishing(HC-MRF), is proposed in the present study to reduce the surface roughness (Ra) (~up to a few nanometer) without affecting the surface topography of the workpiece. HC-MRFsimultaneously utilizes the synergic action between Magnetorheological Finishing (MRF) and chemical etching to reduce surface finishing time and escalate process efficiency. Herein, the carrier medium of the Magnetorheological(MR) fluid is replaced by a reagent to facilitate the chemical etching process, and its synchronized action with mechanical abrasion reduces surface irregularities. Furthermore, the design of the developed apparatus to enable the HC-MRFprocess, where permanent magnets are used to produce the desired external magnetic field, is also discoursed. A case study on the surface roughness enhancement through the HC-MRFon the WC-Co (tungsten carbide in a cobalt-rich matrix) is investigated using Response Surface Methodology(RSM). Herein, Murakami's reagent is used as the carrier medium in the MRfluid, and a reduction in surface roughness(Ra) from an initial value of 312.87 nm to a final value of 34.50 nm is noticed. Moreover, the inclusion of Murakami's reagent enhances the process efficiency. The change in surface roughness with and without Murakami's reagent in the MR fluid is 88.97 % and 43.12 %, respectively, for a constant finishing time.

Magnetorheological fluid assisted finishing (MFAF) is a super-surface finishing technique to achieve a mirror-like polished surface that is required in several fields such as biomedical implants, microchannels, optics, etc. The optimal process parameters and appropriate toolpath planning can significantly improve the surface quality of the parts produced by an MFAF process. This paper presents the trochoidal toolpaths for polishing the surface of a biomaterial: Duplex stainless steel (DSS) via the MFAF process. First, an analytical model has been developed to study the forces applied on the magnetorheological fluid chain of the MFAF tool while scanning on a trochoidal path. This model shows that the polishing time reduces and process efficiency increases with the proposed toolpath compared with the conventional ZIG-ZAG toolpath. Then, the experiments are performed to study the geometrical description of the asperities such as surface roughness (Ra), skewness (Rsk), and kurtosis (Rku) on the polished surface via trochoidal toolpath. Developing an analytical model to study the input variables' impact over the responses includes multiphysics and nonlinearity, making it complex. Hence, the response surface methodology (RSM) is used to analyze and optimize the effect of different process parameters over the surface roughness parameters. Finally, the wettability, corrosion, and wear tests are performed to investigate the biocompatibility of the polished surface.

Nowadays, Additive Manufacturing(AM), i.e., the 3D Printing process, is one of the advanced manufacturing processes for making a complex geometry with high accuracy. Additive manufacturing processes are widely used worldwide and are the fastest-growing industrial technology, as any complex structure with minimal wastage of materials can be fabricated. However, poor surface quality is a major limitation of additive manufacturing due to surface defects, including unmelted powder particles, balling, porosity, etc. Laser polishing utilizes remelting and reflowing of the surface irregularities under the influence of a high-power laser source to efficiently improve the surface quality of the additively manufactured parts. Herein, a thin layer of the surface is molten, and because of surface tension, molten material flows from the peak into the valley with no loss of material from the surface. Laser polishing is a CNC-operated surface finishing method, hence an appropriate toolpath strategy is required to produce uniform surface quality on the polished surface. In the present work, the impact of various toolpath strategies, i.e., raster, offset flat, contour parallel, Hilbert, Peano, and spiral, over the final surface quality is analyzed during the laser polishing. The maximum 92% reduction in average surface roughness with uniform surface quality is observed with a fractal-based toolpath strategy, i.e., Peano with improved surface hardness. Moreover, laser polishing is capable of reducing all surface defects from the fabricated surface, as observed from the scanning electron microscope. Furthermore, an insignificant change in the surface composition of the material is observed after the laser polishing.

The sustainability of biomaterials relies on their interaction with the proteins, fluid, and cells present inside the human body. The biomaterials’ enhanced surface roughness parameters and mechanical properties (i.e. wear resistance) are responsible for reducing degradation (i.e. corrosion rate) to enhance life span during musculoskeletal interaction. The present study compares the biocompatibility between two biomaterials (i.e. Ti-6Al-4V and DSS) polished through the Magnetorheological Fluid Assisted Finishing(MFAF) process. MFAFprocess can produce nano-level average surface roughness(Ra) and is used to improve the quality of the biomaterial's surface. However, apart from Ra, two other surface roughness parameters, namely skewness(Rsk) and kurtosis(Rku) analyze the characteristics of the irregularities formed on the polished surface. During the MFAF process, Trochoidal, a high-speed surface finishing toolpath, is used to map the workspace on the Duplex Stainless Steel(DSS) and Ti alloy (Ti-6Al-4V) biomaterials to enhance their biocompatibility with a reduced finishing time. However, during the pin-on-disc wear tests, an Ultra High Molecular Weight Polyethylene(UHMWPE) is used as the disc to imitate the interface of the bone with the implants for analyzing wear resistance. During experimentation, it is observed that the wear resistance of DSS and Ti-6Al-4V is improved to 3.19 × 10−6and 0.123 × 10−5mm3/min from its initial value of 7.65 × 10−6and 2.68 × 10−5mm3/min, respectively. Furthermore, the dependency of initial surface roughness parameters over the wear resistance of the biomaterials is also analyzed. A three-electrode-based electrochemical test with 0.5 M NaCl concentration is utilized to replicate the human body fluid while analyzing the corrosion resistance of the biomaterials. It is observed that the MFAF process enhances the corrosion resistance of the DSS and Ti-6Al-4V to 0.0037 and 0.0114 mm/year, from its initial values of 0.0079 and 0.0130 mm/year, respectively.