Articles written in Sadhana

    • Optimization in CNC end milling of UNS C34000 medium leaded brass with multiple surface roughnesses characteristics

      Bharat Chandra Routara Saumya Darsan Mohanty Saurav Datta Asish Bandyopadhyay Siba Sankar Mahapatra

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      The present study highlights a multi-objective optimization problem by applying utility concept coupled with Taguchi method through a case study in CNC end milling of UNS C34000 medium leaded brass. The study aimed at evaluating the best process environment which could simultaneously satisfy multiple requirements of surface quality. In view of the fact, the traditional Taguchi method cannot solve a multi-objective optimization problem; to overcome this limitation, utility theory has been coupled with Taguchi method. Depending on Taguchi’s Lower-the-Better (LB) response criteria; individual surface quality characteristics has been transformed into corresponding utility values. Individual utility values have been aggregated finally to compute overall utility degree which serves as representative objective function for optimizing using Taguchi method. Utility theory has been adopted to convert a multi-response optimization problem into a single response optimization problem; in which overall utility degree serves as the representative single objective function for optimization. The study of combined utility theory and Taguchi method for predicting optimal setting. Based on Taguchi’s Signal-to-Noise ratio (S/N), analysis has been made on the overall utility degree and optimal process environment has been selected finally which corresponds to highest S/N Ratio. Optimal result has been verified through confirmatory test. The case study indicates application feasibility of the aforesaid methodology proposed for multiresponse optimization and off-line control of multiple surface quality characteristics in CNC end milling.

    • Powder-mixed electro-discharge machining performance of Inconel 718: effect of concentration of multi-walled carbon nanotube added to the dielectric media


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      The present work reports an experimental investigation on Powder-Mixed Electro-Discharge Machining (PMEDM) of Inconel 718 superalloy using Multi-Walled Carbon Nanotubes (MWCNTs) dispersed in kerosene, as dielectric media. Effects of variation of peak discharge current along with concentration of carbon nanotubes in the dielectric fluid are studied in purview of machining performance indicators including material removal efficiency, tool wear rate, and surface integrity of the machined part. The obtained results are compared to that of conventional EDM which utilizes kerosene as dielectric media. Morphology and topography, these two aspects of machined surface integrity are deliberated. The following surface morphological features: uneven fusion structure, globules of debris, molten metal deposition, surface cracks, pockmarks, and recast layer are identified. Topographical study includes surface roughness, severity of surface cracking, recast layer thickness, transfer of foreign elements, surface metallurgical characteristics, residual stress, and microindentationhardness. It is observed that application of MWCNT mixed dielectric media substantially improves EDM performance of Inconel 718 over conventional EDM. This is due to excellent thermo-physical properties of carbon nanotubes.

    • Machinability of Ti-5Al-2.5Sn for electro-discharge machining: an experimental investigation


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      Present work attempts to investigate machinability of Ti-5Al-2.5Sn for Electro-Discharge Machining (EDM). Extent of machinability is determined through material removal efficiency, tool wear rate, and surface integrity of the EDMed specimen of Ti-5Al-2.5Sn. Detailed analysis of surface morphology followed by study of surface topographical features including surface roughness, crack density, thickness of the recast layer, foreign material migration, metallurgical phase, residual stress, and micro-indentation hardness are carried out. Disappointing morphology is noticed for EDMed work surface at higher values ofpeak current as well as pulse-on time values. It is experienced that occurrence of surface cracks depends on recast layer thickness. As compared to ‘as received’ workpiece exhibiting compressive residual stresses, tensile stresses are found induced after performing EDM operation. Similar phenomenon is experienced incase of tool electrode. EDM operation improves microhardness of the machined surface. For Ti-5Al-2.5Sn,such improvement is nearly three times than that of ‘as received’ work material. During EDM operation on Ti-5Al-2.5Sn, titanium carbide is formed over tool as well as work surface. Formation of such hard carbidesmay degrade machining efficiency

    • Machining performance of Ti6Al4V under dry environment, pressurized air supply and water-MQL: analysis of machininginduced vibration signals and captured thermographs


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      In the present investigation, machining performance of Ti6Al4V is studied under dry environment, pressurized air supply and distilled water based Minimum Quantity Lubrication (MQL). Machining (turning) performance is assessed in purview of cutting force (tangential component) magnitude, tool-tip temperature,width of tool flank wear progression, morphology of evolved chips and severity of vibrations at varied cutting speeds as well as cooling media. Characteristic features of spatial temperature distribution profile (at the vicinity of tool-tip) as influenced by varied cooling media are studied with the help of thermographs of the cutting zone. Mechanisms of cutting tool wear are studied as well. It is experienced that amongst three cutting environments tested, application of water-MQL is beneficial for machining of Ti6Al4V at low cutting speed. Severity of vibrations gets 50.39% reduced during machining under water-MQL than dry condition. Consequently, as compared to dry machining, water-MQL causes 79% reduced tool flank wear and 82% reduced crater wear at low cutting speed. Under water-MQL, reduced tool-tip temperature (66% reduced than dry condition) suppresses severity of tool wear. In comparison with high cutting speed, performance of water-MQL is found much better at low cutting speed. ‘Unaffected zones’ are identified at the worn-out tool rake face under water-MQL. High amplitude of vibration (maximum absolute mean value) causes low chip-segmentation ratio. On the contrary, chip reduction coefficient gets truncated with decrement in vibration amplitude. Vibration amplitude has positiveinfluence on degree of chip-curl.

    • Experimental studies on dry machining behavior of Ti-6Al-4V using carbide, cermet, and SiAlON tools


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      Traditional dry machining of ‘difficult-to-cut’ titanium alloy Ti-6Al-4V has always been a challenging task. This is due to its lower thermal conductivity, strong work-hardening tendency, and extreme chemical reactivity. These causes adverse machining effects including premature tool failure, evolution of hugecutting temperature, machine tool chatter, and disappointing surface integrity of the machined work part. Selection of compatible tool material, appropriate tool geometric parameters, and adequate control of cutting parameters are of vital importance towards achieving satisfactory machining yield. In this context, performances of MT-CVD TiCN/Al2O3 bi-layered coated carbide, PVD TiN/TiCN/TiN multi-layered coated cermet, and CVD TiCN/Al2O3 bi-layered coated SiAlON inserts are studied during dry machining of Ti-6Al-4V within cutting speed range 50-130 m/min; at constant feed ~ 0.1 mm/rev, and depth-of-cut ~ 0.35 mm. Approximate tool-tip temperature (maximum value) attained during operation, magnitude of tangential cutting force, and width offlank wear progression are measured. Detailed study on wear morphology of worn-out inserts, chip’s micro/ macro morphology, and surface integrity of the machined product are carried out. It is experienced that cermet tool performs better than remaining two counterparts in purview of lower tool-tip temperature, reduced flank wear, and better machined surface integrity.

    • Comparative experimental study on application feasibiility of MTCVD TiCN-Al2O3-TiOCN multi-layer coated carbide and PVD TiN single layer coated composite ceramic inserts during dry machining of Ti-6Al-4V


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      Due to high temperature strength (hot strength), excellent corrosion resistance and high strength-toweight ratio, Ti-6Al-4V alloy is considered as a potential candidate for extensive applications in aerospace and biomedical engineering. But, alloy's low thermal conductivity and extreme chemical affinity (towards toolsubstrate and coating materials) often cause an aggressive cutting environment with a tremendous rise in cutting zone temperature, premature tool wear, and disappointing surface integrity during conventional machining processes. In order to achieve desired machining yield without opting for any coolant, selection of proper cutting tool (based on their geometry and properties) is indeed vital. Thus, the present work examined the performance of MTCVD-TiCN-Al2O3-TiOCN multi-layer coated carbide and PVD TiN single layer coated compositeceramic (Al2O3/TiCN) tool inserts during dry machining of Ti-6Al-4V. Higher friction coefficient (of the coating system) was revealed for the ceramic tool which caused substantial temperature rise at tool-tip. On the other hand, carbide insert imparted lower cutting force (beyond ν = 80 m/min) than ceramic insert due to its better thermo-chemical stability. Coating peel-off and tool flaking were witnessed for ceramic insert due to its thermal instability at higher cutting speeds; while carbide tool was mainly affected by material adhesion,abrasion, and chip fusion (adhesion of broken chip-fragments over tool surface due to high pressure and temperature). It was experienced that induced cutting heat significantly affected chip morphology under a dry cutting environment. Up to ν = 130 m/min, ceramic tool exhibited lower flank wear than carbide tool.

    • Machinability of Inconel 825 under nano-Al2O3 based nanofluid minimum quantity lubrication


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      In the present work, turning performance of Inconel 825 superalloy is studied under Nanofluid Minimum Quantity Lubrication (NFMQL). Nanofluid used is nano-Al2O3 dispersed distilled water. The tool insert used in this study is PVD multi-layered (TiN/ TiCN/ TiN) coated cermet. The following machiningperformance indicators: tangential cutting force, tool-tip temperature, wear morphologies of the tool insert, macro/ micro-morphologies of chips produced, etc. are studied. It is observed that dry machining environment causes vibration signals of random nature whose frequency and amplitude of acceleration are highly timevariant. On the contrary, periodic vibration signal with lower amplitude of acceleration is detected in case of NFMQL machining. Consequently, NFMQL exhibits lower cutting force, reduced tool-tip temperature, and less severe tool wear than that of dry machining. NFMQL produces thinner chips with shorter segmentation spacing and wider shear angle than dry machining.

    • Performance of uncoated/coated carbide inserts during MQL (sunflower oil) assisted machining of Inconel 718 superalloy


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      In the present work, the machinability of difficult-to-cut Inconel 718 aerospace superalloy is studied under vegetable oil-based minimum quantity lubrication (MQL) in consideration with different cutting tool materials. MQL environment is produced by supplying air-oil mist in which biodegradable sunflower oil is used.In comparison with uncoated carbide tool, performances of MT-CVD multi-layered TiCN-Al2O3-TiOCN coated and MT-CVD double-layered TiCN-Al2O3 coated carbide inserts are assessed during longitudinal turning of Inconel 718. Coating materials are characterized by average thickness of individual coating layer, elemental composition and frictional coefficient. With constant feed and depth-of-cut (0.1 mm/rev and 0.25 mm respectively), quantitative responses such as tangential cutting force, tool-tip temperature and width of tool flank wearare considered as machinability assessment criteria under varied cutting speed condition (v = 60, 80, 100 and 130 m/min). Notable reduction in tool-tip temperature (25.6% and 30.4%) and reduction in cutting forces (10.6% and 22.3%) are obtained for coated tool [T1] and coated tool [T2] respectively, when compared to uncoated counterpart. Detailed analysis on tool wear modes is carried out followed by chip’s macro/micromorphology. Apart from chip’s micro-morphological parameters, morphologies of chip’s back and free surfacesand chip microhardness are studied.

    • Parametric studies of fused filament fabrication towards fabrication of 2D auxetic metamaterial cellular structure followed by auxeticity simulation


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      As compared to conventional materials, auxetic metamaterials correspond to cellular structures with low density and better mechanical properties. Mechanical properties of auxetic metamaterials are influenced by both the base material and the geometry (topology) of the unit cell. The high strength-to-weight ratio and tunable mechanical properties of auxetic structures make them suitable for wide engineering applications. In this work, auxetic behavior of novel chiral honeycomb structures (anti-tetra chiral) is studied using Finite Element Method(FEM). In addition, fabrication of a few tensile specimens is carried out by Fused Filament Fabrication (FFF). FFF is an efficient rapid prototyping technology which offers design freedom to fabricate complex geometrical structures (difficult or impossible to manufacture through conventional routes). Several FFF parameters do influence part quality and process performance. In order to study effects of process parameters on part quality (tensile strength, roughness, material consumption) and build time, tensile specimens are fabricated at different build orientations and build styles (dense and sparse). Fractured surface morphologies are observed through scanning electron microscopy to understand the bonding pattern between the layers of FFF parts. Finally, anappropriate combination of FFF parameters is determined through Technique for Order Preference by Similarity to Ideal Solution (TOPSIS) to ensure the maximum part tensile strength, the minimum part surface roughnessand the minimum build timing. Finally, an auxetic anti-tetra chiral candidate specimen of ABS plastic is built through FFF. From finite element simulation, the Poisson’s ratio of anti-tetra chiral 2D structure is found to be close to -1. Poisson’s ratio of anti-tetra chiral 2D honeycomb is found insensitive to the dimensionless topological parameter (i.e. ratio of ligament length-to-node radius). It is experienced that part tensile strength decreases with increase in build orientation angle as well as the air gap (from ‘dense’ to ‘sparse’ building style). The build time of FFF parts depends on the height of the part along the build direction. FFF part fabricated using ‘dense’ build style at 45° build orientation exhibits the best quality and corresponds to the minimum fabricationtime.

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