Department of Mechanical engineering

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Author: search.filters.author.Roy, TribeniSubject: search.filters.subject.Mechanical Engineering

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    Analysis of material removal mechanism in nanoscale machining of copper
    (Sage, 2024-01) Sharma, Anuj; Roy, Tribeni
    In the current study, molecular dynamics modeling and simulation are carried out to analyse mechanisms in tool-workpiece interaction in nanoscale cutting. Various combinations of a/r ratios for constant r (r = tool edge radius and a = uncut chip thickness) are considered and different crystal orientations of the workpiece specimen are employed in the nanoscale cutting model. From the simulation, material anisotropy behavior is observed during the nanoscale cutting of copper material. Analysis at the molecular scale reveals that the crystal orientations family {1 1 0}<1 0 0> is hard to machine and the family of crystal planes {1 1 1}<1 1 0> is easiest to cut. While comparing in different crystal planes and directions, it was noticed that the material deformation in nanoscale machining takes place only in slip directions, that is, <1 1 0> family of directions. It is also found that as the uncut chip thickness is decreased, the cutting mechanism changes from shear plane cutting to plowing to sliding in Cu.
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    Molecular dynamics modelling of micro/nano manufacturing processes
    (Sage, 2024) Sharma, Anuj; Roy, Tribeni
    Manufacturing processes such as machining, casting, welding, forming including additive manufacturing are essential processes to fabricate various types of components. These manufacturing processes have been developed and are improving with time by optimising process parameters and revealing better insights about the processes. Earlier, research has used various tools like finite element analysis, mathematical modelling, etc., to improve the process understanding and their optimisation. This has brought the significance of computational modelling to support the analysis and optimization of manufacturing processes. In general, any manufacturing process works on two different domains of size scale such as micro scale and macro scale mechanism. Micro scale mechanism is associated with micro/nano manufacturing processes which differs from the macro scale, and conventional tools of modelling do not support it. During the last few decades, there has been an increasing interest in the simulations of micro/nano manufacturing processes. Modelling at nano scale brings out deep insights into the mechanisms and different phenomena. Out of the various modelling approaches, Molecular Dynamics (MD) modelling approach is the most preferred technique to simulate nanoscale manufacturing and investigate the science behind the processes. In general, MD simulation was extensively being used in the field of biology and chemistry towards discovery of novel drugs, chemical, materials, etc. In the last few decades, MD simulation has also been implemented by researchers in the field of manufacturing especially for polishing and thin film technology. Recently there has been a demand to use this tool to discover all possible phenomena at the atomic scale for all types of manufacturing processes. In this special issue of the Journal of Micromanufacturing, recent findings in micro/nano manufacturing through molecular dynamics modelling are aimed. In MD simulation, materials are modelled from atoms by assuming the atoms obey Newton’s second law of motion and will interact using interatomic potential. This concept of modelling brings insight into the manufacturing processes at atomic scale. However, modelling materials at the atomic scale requires reducing the temporal resolution of the order of a few picoseconds. Thus, the computational effort and time become enormous when any process is being modelled at a nanometric scale. Moreover, this approach becomes impossible to model when the space frame is in order of a few microns or more. To overcome this issue, researchers have identified alternate approaches like coarse grain modelling, multi-scale modelling, atom to continuum modelling, etc. All these techniques utilise the MD modelling at the zone of interaction and due to this, the special issue has focussed on MD simulation related novel outcomes for various types of manufacturing processes such as nanofinishing, nanomachining, additive manufacturing, nano-indentation, material’s mechanical characterisation, etc. In addition, this Special Issue will also promote and disseminate the latest works focused on MD modelling and simulation of various micro/nano-manufacturing processes and encourage researchers to adopt this technique to cater the present and future demand of technology. A brief report about the articles accepted under this issue are summarised as follows.
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    Dataset for "Strain induced electrochemical behaviours of ionic liquid electrolytes in an electric double layer capacitor: Insights from molecular dynamics simulations"
    (Zenodo, 2020-10) Roy, Tribeni
    The datafile contains molecular dynamics simulation results for analysing the electrochemical behaviour of ionic liquid based EDLC under compression and tension.
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    Pulsed Electric Field Based Material Removal in Microelectrical Discharge Machining
    (COMSOL, 2016) Roy, Tribeni
    Micro electrical discharge machining (MEDM), a scaled down version of EDM process, is a micro machining process used to fabricate micro holes and intricate shapes in electrically conductive materials irrespective of its hardness. In this process, an electric spark is generated in the gap between the two electrodes (tool as cathode and workpiece as anode) submerged in dielectric that leads to a plasma formation, which eventually leads to material removal by melting and vaporization. The mechanism of material removal in MEDM is a very complex process and hence has not been understood fully. Simulation of material removal has been carried out in this study by using COMSOL Multiphysics® software to understand the behavior of pulsating electric field in MEDM. Assuming a constant heat flux, it has been shown that material removal takes place whenever the electric field strength at any particular location on the workpiece crosses the threshold value.
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    Recast Layer Thickness Characterization of Array of Micro Features Using X-Ray Micro Computed Tomography
    (SSRN, 2018-02) Roy, Tribeni
    Destructive characterization of recast layer on reverse micro EDM-ed (RMEDM) surface renders the component unusable for its intended application. X-ray micro computed tomography (µCT) is a non-destructive technique widely used for characterization of internal structures of different materials. Array of hemispherical shaped micro features fabricated by RMEDM by employing taper ended blind holes led to variation in recast layer thickness of the micro features both along its length and position on the surface of workpiece. µCT characterization of recast layer thickness revealed that with respect to location on micro feature, the tip of micro feature had the highest recast layer thickness and the base the lowest. Also, with respect to location of micro feature on the surface of workpiece, the micro feature at the periphery had the lowest recast layer thickness whereas the micro feature at the centre had the highest.
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    Investigation of tool-workpiece interaction in nanoscale cutting: a molecular dynamics study
    (Inder Science, 2019) Roy, Tribeni; Sharma, Anuj
    Ductile and brittle materials differ in their physical and mechanical properties and pose distinct interaction with the cutting tool while nano-machining. It is thus imperative to analyse the mechanism of material removal and tool-workpiece interaction. Towards this, molecular dynamics simulation (MDS) is carried out to study the diamond tool and workpiece interaction in the nanoscale cutting of Cu (ductile material) and Si (brittle material). Results show that material removal in Cu takes place through shear deformation by dislocations formation and their propagation while in case of Si, it takes place through phase transformation of the material in cutting zone. Force analysis of both the materials shows that machinability of Cu in nanoscale cutting is better compared to Si. Furthermore, tool wear while machining of Si with sharp edge tool is due to chipping whereas radial distribution function reveals that graphitisation of the round edge tool occurs during machining of Si.
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    Fabrication, characterization and comparative analysis of mechanical properties of micro features generated by reverse micro EDM
    (Springer, 2019-07) Roy, Tribeni
    Moderate to high aspect ratio micro features (projected) finds wide application in MEMS components, fuel cells for micro reactors, sensors and actuators, micro optical components etc. Reverse micro electro discharge machining (RMEDM) is one of the extensively used process for fabricating such micro features. The present authors have already developed a technique for generating different shapes and sizes of micro features by suitable modification of tool in RMEDM. Mechanical properties like hardness and elastic modulus of these micro features play a significant role in determining their suitability for various applications. Therefore, the objective of this paper is (a) to generate projected micro features corresponding to tapered blind hole depths of 0.1 mm and 0.3 mm using RMEDM and (b) to determine the effect of tapered blind hole depth on the hardness and elastic modulus of the projected micro features. Hardness and elastic modulus were measured using nano indentation technique. Results indicate that starting from the periphery, both hardness as well as elastic modulus first increase (presence of recast layer) and then decrease (presence of heat affected zone) for projected micro feature corresponding to 0.1 mm hole depth before attaining the properties of the parent material. Due to high amount of debris agglomeration in case of 0.3 mm hole depth, high amount of abnormal discharges occur which do not provide sufficient time for the formation of thermally softened layer as was in the case of micro feature corresponding to 0.1 mm hole depth. Hardness, therefore, is always high starting from recast layer to the HAZ before finally attaining the hardness of the parent material. Debris agglomeration did not have much influence on the elastic modulus and the variation of elastic modulus of the micro feature corresponding to 0.3 mm hole depth remains fairly uniform a compared to the parent material.
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    Corrigendum to “Postulation of optimal charging protocols for minimal charge redistribution in supercapacitors based on the modelling of solid phase charge density
    (Elsevier, 2021-08) Roy, Tribeni
    The authors regret that the model equations and the model codes used in the original article contained errors. Specifically, Eq.(20) of the original article omitted a liquid phase electrical potential term. Further, the parameters used in the original model codes were subject to input errors which were later determined to produce erroneous results. The model equations, input parameters and model codes have been corrected and are presented in this Corrigendum. For the most part, the qualitative results and conclusions are similar to those presented in the original article. However, the corrections have led to significant changes to the results on which the analysis conducted in section 3.5 was based. As a consequence, the results presented and the conclusions drawn therein have been subject to major revisions.
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    Electrical Discharge Diamond Grinding
    (CRC Press, 2022) Roy, Tribeni
    The current requirement for complex systems has prompted the development of novel materials that are both strong and lightweight. Machining complex shapes on these materials is always a difficulty. Also, it is challenging to achieve satisfactory results with a single machining process. As a result, hybrid machining processes are commonly utilized to achieve excellent precision and polish. Electrical discharge diamond grinding (EDDG) is an example of a hybrid process that combines the benefits of both EDM and mechanical grinding. Hard and brittle conductive materials are softened by electrical discharges, which is followed by mechanical grinding to remove the softened layer. EDDG eliminates the difficulties associated with EDM (such as recast layer, heat-affected zone) and scratching due to excessive grinding forces. This chapter provides an overview of mathematical models used in the EDDG process to predict cutting forces and material removal.
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    Mechanism of material removal on stainless steel through diamond abrasion: a molecular dynamics simulation study
    (MTT, 2023) Roy, Tribeni; Sharma, Anuj
    A rough surface of any engineering material exhibits high surface energy which results in higher potential energy or cohesive energy of the material, and it affects both optical as well as chemical properties. In this paper, stainless steel 304 (or SS304) is selected for nano-finishing through diamond abrasive using MD simulations. It is found that the diamond abrasive creates new bonds with Cr and Fe atoms by rise in local temperature and stresses. Moreover, Ni atom diffuses inside the abrasive as it does not chemically bond with C atom. The abrasion on steel due to diamond also leads to phase transformation on both abrasive as well as the workpiece. Subsequently, the transformed phase is removed from the workpiece due to the newly formed chemical bonds, however, in the process, the abrasive particle deteriorates by phase transformation and materials loading. Thus, the present study is useful in optimising