In the present research, a composite layer of TiO₂-TiC-NbO-NbC was coated on the Ti-64 alloy using two different methods (i.e., the electric discharge coating (EDC) and electric discharge machining processes) while the Nb powder were mixed in dielectric fluid. The effect produced on the machined surfaces by both processes was reported. The influence of Nb-concentration along with the EDC key parameters (Ip and Ton) on the coated surface integrity such as surface topography, micro-cracks, coating layer thickness, coating deposition, micro-hardness has been evaluated as well. It has been noticed that in the EDC process the high peak current and high Nb-powder concentration allow improvement in the material migration, and a crack-free thick layer (215 μm) on the workpiece surface is deposited. The presence of various oxides and carbides on the coated surface further enhanced the mechanical properties, especially, the wear resistance, corrosion resistance and bioactivity. The surface hardness of the coated layer is increased from 365 HV to 1465 HV. Furthermore, the coated layer reveals a higher adhesion strength (~118 N), which permits to enhance the wear resistance of the Ti-64 alloy. This proposed technology allows modification of the mechanical properties and surface characteristics according to an orthopedic implant’s requirements.

Single point diamond turning is one of the ultraprecision methods to generate high quality surfaces with highest possible profile accuracies. However, diamond turning process also introduces some unique errors which affect the surface finish. Some of these errors are controllable, while some are noncontrollable. Controllable parameters need proper selection, whereas uncontrollable parameters require adequate understanding of the process behavior. In this study only the effect of uncontrollable parameters on surface finish is explored. Tool overhang results tool–workpiece vibration whereas dynamic unbalance of vacuum responsible for workpiece wobble and both affect the surface finish considerably. Chipping of tool edge, improper extraction of chips, and slipping of workpiece on vacuum chuck are the main reasons of random scratch marks on surface and are contributing factors for degradation of surface finish.

Freeform surfaces are gaining popularity in vast engineering applications including optical engineering, aerospace, automotive, and biomedical. Success of freeform surfaces lies with its complex design and fabrication methods. Ultraprecision machining is the most suitable process to develop the complex shapes with nanometric surface finish. Slow tool servo (STS) arrangement of ultraprecision machining is controlled by interrelated motion of three axes (CXZ). The quality of freeform surface generation by STS process has direct association with selection of its input process parameters, i.e. X-axis motion increment, C-axis angular increment, depth of cut, tool nose radius, and spindle speed. In this paper, the optimization techniques are adopted to understand the weightage of individual machining parameters and the optimum range of these input parameters are found to achieve the desired surface finish. Further, detailed experimental investigations are carried out for in-depth understanding of the effects of these individual parameters in relation to fabrication of freeform profile. By utilizing the optimized process, the profile accuracy of 0.82 µm, three-dimensional surface finish (S_a) of 26 nm, and two-dimensional surface finish (R_a) of 11.6 nm are achieved in very first cut. The investigation helps to understand the relationship between the STS machining parameters and the achieved surface finish and profile accuracy of freeform optics.

This article presents the use of Fiber Bragg Grating (FBG) sensor to measure the temperature induced at the tip of the tool, while micro-face turning of optical surfaces. FBG sensor of 120 μm diameter was mounted near the tip of the tool and the shift in Bragg wavelength due to induced temperature was acquired with the help of an interrogator. The experiments were conducted on a Taylor Hobson DT-250 SPDT machine, over three different optical grade alloys namely Aluminum 6061, OFHC (Oxygen free highly conducting) copper and stainless steel. It was observed that while machining stainless steel, temperature at tool tip was highest and in case of OFHC copper it was lowest. The roughness and waviness of machined optical surfaces were measured using PGI 400 Profilometer. The results confirm that temperature induced in micro cutting and the rate of heat dissipation of work material contributes significantly to optical surface integrity.

Burnishing is a cold working technique used as a surface enrichment to meet the desired surface properties of the workpiece. It improves the visual properties, dimensional tolerances, fatigue strength, surface roughness, and hardness of the work material by applying appropriate pressure through a complex ball burnishing tool to cause plastic deformation. In the current work, the mathematical modeling of the burnishing process was carried out to predict surface roughness by considering the process parameters such as contact radius, penetration depth, and elastic rebound. Further, a customized tungsten carbide (W.C.) insert having a hardness of 80 HRC was developed for the burnishing operation. The micro-hardness of the resulting burnished surface improved from 44 to 48 HRC. The surface quality of the tungsten carbide insert improved by up to 17.1 nm through polishing. Several experiments were performed by selecting appropriate process parameters using developed model feedback. The surface quality of the workpiece improved by up to 45 nm, which resulted in automatic improvements in fatigue strength up to seven times that of the virgin material. The results predicted from the mathematical model were in good agreement (less than 5% deviation) with the experimental results. This study helps to understand the surface formation mechanism in the burnishing process in more detail. Additionally, the achieved results show a significant improvement in the surface finish (~95%), indicating the potential of the burnishing process and how fast and cost-effective it is. The novelty of this paper lies in the improvement in surface roughness and the validation of our mathematical model results with the experimental results.