Additive manufacturing techniques are replacing conventional subtractive machining processes; however, the surface quality and defects have been a key roadblock to expanding AM’s uses. This paper describes experimental investigations in the high-speed dry machining and additive manufacturing (AM) of titanium alloy (Ti6Al4V), discussing the effect of machining and AM conditions on the surface characteristics due to the micro-deformation layer. Analysis of the machined surfaces shows the deposition of microparticles at a high cutting speed of 170 m/min at moderate feed rates. The predominant thermal softening effect at a high cutting speed causes restructuring of the micro-deformation layer. Thus, the machined surface shows fewer alterations and a correspondingly lower surface roughness. A high cutting speed also favors the induction of high residual stresses that are compressive. Shallow grooves are seen throughout the surface along the feed spacing with a higher depth of cut of 0.8 mm. An increase in the cutting speed from 170 m/min to 190 m/min leads to a 61% increase in the surface finish owing to a rise in machining temperature leading to thermal softening, and subsequent restructuring of the machined surface layer occurs. For the feed rate, the surface finish values decrease gradually as the feed rate increases, and the worst finish of 1.37 µm is attained at a feed rate of 0.875 mm/rev. This study also compares different AM processes for Ti6Al4V based on the defects and their effects on mechanical properties, such as tensile and fatigue strength. It was observed that the ultimate tensile strength and the yield strength were approximately 20% more in SLM and direct energy deposition as compared to electron beam melting. The mechanism of these effects is also explained by elaborating on the influence of grain size, phase, and other microstructural behaviors on the final mechanical properties of the produced part.
Abstract:In this work analysis of fundamental aspects of orthogonal microcutting was carried out in terms of variables like shear angle, chip thickness, chip morphology as a function of cutting speed, depth of cut, tool rake angle and heat treatment provided to the work specimen. Analysis of results shows that the material flow pattern at low cutting speed is highly inhomogeneous, which affects segmented chip formation. As the uncut chip thickness approaches the minimum chip thickness, chips are formed by shearing of the workpiece, with some elastic deformation still occurring.At the highest depth of cut of 100 µm, shear angle is fairly dependent on the rake angle. AISI 1215 steel heat treated at 1200C, shows the lowest shear angle at all the depths of cut at 5 or 10 of rake angle. Analyses of chip segment per unit length show that, the number of segments reduces as the rake angle increases for all the four work materials that were heat treated at the various temperatures.
Manufacturing of aspheric profile of lens at nanometric level is difficult but the measurement and evaluation of metrology parameters is still a bigger challenge. For successful results of the lens systems, precise and defect free lenses are required. The manufacturing conditions have direct effect on the metrological parameters. For appropriate evaluation of metrology parameters, proper interpretation of aspheric surface parameters must be known. . In this study, the mechanical parameters, such as radius of curvature, slope error, tilt, centre thickness, and sag value of lens, were measured by using contact type form talysurf, non-contact type fizeau interferometers, and other instruments. The experimental results reveal that an increase in the spherical aberration is caused by increasing the lens thickness beyond 4.995mm or by increasing the radius of curvature beyond −13.8396mm or by increasing the aspheric higher order coefficients. Also its dependencies on the diameter of least confusion is studied.
The implantation of stents and instruments with capillary action demands super-finished internal surfaces of the manufactured product. Elasto-abrasives magneto-spiral finishing (EAMSF) enhances the productivity of finishing by incorporating the abrasive flow in spiral motion due to the presence of the magnetic field. Here, novel impregnated elasto-magnetic abrasive particles (IMPs) are used in a magnetic field-assisted environment to polish the inner walls of the workpiece. In EAMSF, magnetic force provides excess finishing pressure to the abrasives whereas the elasticity of the high impact polystyrene (HIPS) absorbs the excess force of the IMPs on the finishing surface. An indigenous mathematical relation taking into account the physics of process indicating material removal shows a close resemblance to the experimental results with an error percentage of 1.03 has been developed. The results of experimentation revealed that with 50% concentration of abrasives and a magnetic field density of 18mT yields, a superior surface finish with a Ra value equal to 0.053 μm and maximum material removal of 6.9 mg; while in the absence of a magnetic field, superior surface finish with a Ra = 0.266μm and maximum material removal of 5.4 mg is achieved. In the presence of magnetic field density, significant enhancement of material removal, surface finish, and burr removal is observed. Finishing of the surface at 50% abrasive concentration with a magnetic field represents regular finishing and the trench marks present in the original surface are removed after finishing.
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