Shunmugam M S

High-aspect-ratio high-quality microholes are required in turbine blades to improve cooling performance. These cooling holes are drilled by pulsed laser and hence dimensional as well as geometrical tolerances like circularity and cylindricity are important. The measurement of geometrical features of the microholes is a very challenging task without destroying the components. In the present work, the microholes are produced on Ti6Al4V alloy by ultra-short pulse laser. The geometrical features of microholes are then captured using a non-destructive technique, namely computed tomography. CT-scanned 3D data is directly used for geometrical analysis using open-source software, GOM Inspect. Since algorithms used in the GOM Inspect are proprietary in nature, the extracted coordinate data are also analyzed using the computational methods developed by the authors based on least squares technique. The dimension, circularity, and cylindricity of microholes are compared with the results obtained from GOM Inspect software and a close match is found.

In this work on electrical discharge machining (EDM), pulse characteristics and pulse types are assessed from the pulse trains using a novel thresholding approach. For the first time, discharge energy is derived from the pulses, instead of using the setting voltage, setting current and duty cycle. Specific energy is computed as the discharge energy required for removing unit volume of work material. The experiments are carried out on D3 die steel and the specific energies are determined for conventional, powder-added and ultrasonic-assisted EDM. The maximum specific energy increases from 406.6 J/mm3 in conventional EDM to 463.1 J/mm3 with powder mix, while it reaches 486.8 J/mm3 with ultrasonic assistance. However, only the powder mix increases the maximum material removal rate (MRR) from 0.384 to 0.464 mm3/s. The ultrasonic-assisted EDM results in a marginally reduced maximum MRR of 0.369 mm3/s, even though the specific energy is the highest.

This chapter highlights the fundamental deformation and fracture mechanism of an engineered ultrafine-grained (UFG) material developed by a combination of cryorolling and short-annealing treatment. The UFG material developed by cryorolling possesses superlative tensile strength. However, the ductility and strain hardening potential of the material is found to be low, reducing its manufacturing capabilities. Controlled post-deformation annealing results in a combination of good strength and ductility. The anisotropic property of the material is also improved after short-term annealing. These properties have been attributed to the unique equiaxed, thermally stable microstructure comprising of high-angled nanometric grains. The various mechanical properties have been experimentally evaluated by performing the tensile test at all three different processing conditions (base, cryorolled, annealed) and the corresponding strain hardening potential, fracture behaviour and anisotropic properties have been systematically investigated. These properties have been correlated with the microstructural features of the material. This has been achieved by mechanical testing and characterisation of the material by employing transmission electron microscopy, fractographic analysis and determination of mechanical anisotropy coefficient (Lankford coefficient). Finally, a case study on the improved microforming abilities of UFG material over coarse-grained material has been presented.