Department of Mechanical Engineering

Indian Institute of Technology Palakkad&nbsp;(IIT Palakkad or IIT PKD) is a public autonomous&nbsp;engineering&nbsp;and&nbsp;research&nbsp;institute located in&nbsp;Palakkad,&nbsp;Kerala. It was&nbsp;one of the five new&nbsp;IITs&nbsp;proposed in the&nbsp;2014 Union budget of India. The campus was inaugurated on 3 August 2015. The institute has 94 faculty, 978 students, and 63 non-teaching staffs.

IT Palakkad currently offers four-year Bachelor of Technology (B.Tech) and two years MS programmes in 8 different engineering disciplines including&nbsp;Computer Science, Electrical, Mechanical, Civil among others.

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IIT Palakkad

Stationary shoulder friction stir welding (SSFSW) is a new variant of the conventional FSW with rotation of only the tool probe to reduce the rate of heat generation along the tool–workpiece interface and hence, weld joint residual stresses. Studies on the evolution of residual stresses in SSFSW are rare as the process is new. A detailed investigation on the evolution of welding-induced residual stress is reported here for SSFSW and the conventional FSW of four different aluminum alloys. A finite element method–based numerical model, JWRIAN-Hybrid, is used for the three-dimensional heat transfer and thermo-mechanical stress analyses. The computed results are validated extensively with the corresponding experimentally measured results. The results show approximately 10% to 20% reduction in the peak residual stresses in SSFSW under identical welding conditions. © 2019, Springer-Verlag London Ltd., part of Springer Nature.

World University root node

International Journal of Advanced Manufacturing Technology

Probing residual stresses in stationary shoulder friction stir welding process

In recent years, the popularity of nickel-based super alloys has been on the rise due to their widespread application in oil and gas, aerospace and automobile, marine and biomedical industries. The unique combination of superior mechanical and chemical properties like hardness, strength, temperature and corrosion resistance is responsible for the extensive application of these alloys. However, these properties pose challenges during the conventional machining of nickel-based super alloys. The low thermal conductivity and high work-hardening characteristics of Inconel 718 make it difficult to machine. To overcome the aforementioned problem, a hybrid non-contact electrical discharge and arc-machining process has been employed. In this process, an additional DC power supply is employed in conjunction with the normal EDM-pulsed power supply. Furthermore, the selection of proper electrode material plays an important role in defining the machining performance. In this study, in order to select a suitable electrode material for the newly developed process, several experimental investigations have been conducted with three different electrode materials, namely brass, copper (Cu) and copper tungsten (CuW). The results have shown that, for all the current settings, brass electrode provides the highest material removal rate (MRR), followed by Cu and CuW electrodes. However, CuW exhibited the lowest electrode wear rate (EWR). Moreover, the average surface roughness and surface characteristics of the electrodes after machining were investigated as well. Based on all the performance parameters, CuW appears to be the best choice for the hybrid process to machine Inconel 718. © 2019, Springer-Verlag London Ltd., part of Springer Nature.

Ultrafast drilling of Inconel 718 using hybrid EDM with different electrode materials

Computer simulations of a wide range of applications like materials processing, thermal energy storage and conversion systems, nuclear reactors, solar energy, and pollution control, etc. are of high importance in this era. In many of these applications, strong thermo-fluidic interactions between fluid and structures exist. Efficient and accurate numerical modelling of these interactions provide initial predictions of the process, but at times, it becomes challenging where complex shape of the structures is involved. To address this issue, often numerical methods that are proposed suffer lower computational accuracy and complex algorithms to capture interfacial predictions. In this paper, development, accuracy study and robustness of an in-house openMP parallelized Immersed Boundary-Thermal Lattice-Boltzmann (IB-TLB) solver are presented, which is capable of simulating complex boundary problems involving thermal interactions and accurately capture interfacial predictions. The solver showed excellent agreement with literature for a natural convection problem involving eccentrically placed stationary heated cylinder inside a cold square enclosure and forced convection around an iso-thermal circular cylinder. The numerical simulation of moving bodies is already quite a complex problem and the complexity increases further when we introduce heat transfer phenomena in it. Spatial order of accuracy test revealed, the IB-TLB algorithm exhibits first-order accuracy for velocity and temperature errors while pressure error retained second-order accuracy for moving boundary problems. It is also observed that the present algorithm can accurately predict local parameters like coefficient of pressure and Nusselt number with good accuracy and thus possesses promising potential to simulate complex moving boundary problems. The present solver will find its application in a wide range of areas such as heat exchangers, solar energy systems and chemical and food industries etc. © 2020 Institute of Physics Publishing. All rights reserved.

IOP Conference Series: Earth and Environmental Science

Development of an immersed boundary-thermal lattice boltzmann solver for fluid-particle interaction in energy management systems

Current study aims to investigate the effect of machining stability on the surface integrity of the wire electric discharge machined Inconel 718 superalloy. The wire electrode material used for machining is hard zinc coated brass. Experiments were conducted at various levels of machining stabilities, defined with respect to discharge energies and machining gap conditions. The topographical characteristics were analysed by contact surface profilometer and non-contact 3D profilometer. Scanning electron microscope (SEM) images were analyzed to observe and compare the surface defects like microvoids, micro-cracks, micro globules, micro-craters on the samples machined at different stability levels. The least stable machining condition, with highest discharge energy, lowest inter electrode gap and least pulse off time, produced the most uneven topography. Recast layer (RCL) thickness was analyzed by observing the polished cross-sectional view of machined specimens under SEM. The conditions that provided the least RCL thickness were the most stable machining conditions. Furthermore, the surface layer characteristics like elemental contamination and thermal softening effects were analyzed using EDS and micro hardness tester respectively. All these characteristics have close relationship with the degree of machining stability. © 2020 The Author(s).

Fulltext

Procedia CIRP

Surface integrity comparison of wire electric discharge machined Inconel 718 surfaces at different machining stabilities

The study aims to correlate the mean gap voltage variation and wire breakage occurrences during the wire EDM of Inconel 718. A novel approach to predict the wire breakage is introduced by considering the mean gap voltage variation ($\Delta$Vm) as an indicator of the instabilities in the spark gap. Such instabilities are regarded as the primary reason for wire breakages and inferior part quality of wire electric discharge machined components. The parameter $\Delta$Vm is a process data obtained as the difference between servo voltage and mean gap voltage (Vm). It was found experimentally that if the value of $\Delta$Vm crosses a threshold limit, the process interruptions through wire breakages were observed. In order to predict the wire breakage situations, the study models $\Delta$Vm using adaptive neuro fuzzy inference system (ANFIS). Based on central composite design (CCD) of response surface methodology (RSM), 31 experiments were conducted and $\Delta$Vm is recorded as the response. The input parameters considered were pulse on time, pulse off time, servo voltage and wire feed rate. The ANFIS model was found very accurate in predicting $\Delta$Vm, based on which wire breakage alerts can be given. The capability of the model is further confirmed by verification experiments. EDS and microstructural analysis further revealed the effect of $\Delta$Vm on wire wear and part quality. Higher value of $\Delta$Vm resulted in greater wire wear and inferior part quality. The surface finish and flatness error of machined parts were measured to compare the part quality.

CIRP Journal of Manufacturing Science and Technology

ANFIS modelling of mean gap voltage variation to predict wire breakages during wire EDM of Inconel 718

Electrical discharge machining (EDM) is one of the nonconventional machining processes suitable for machining of metal matrix composites (MMC). In this work, the heat transfer model has been adopted to predict temperature distribution within selected MMC and considered other machining conditions also such as temperature-dependent thermal properties, Gaussian heat flux and plasma radius. The MMC (Al–4Cu–6Si+10%SiC) is used as a workpiece material in this present investigation. The FEA finite element analysis (FEA) axisymmetric model was generated to simulate the MMC using FEA package multi-physics and predicted Material Removal Rate (MRR). Also, the results have been validated with experimental results. © 2020, Springer Nature Singapore Pte Ltd.

Advances in Simulation, Product Design and Development

FEA of Electrical Discharge Machining on the Particle Metal Matrix Composite

The behavior of droplets of urea-water-solution (UWS) evaporating under the influence of a hot stream of air was investigated experimentally, under temperatures ranging from 100°C to 400°C. The droplets were suspended on a glass microfiber to minimize the influence of heat conduction, through the fiber, on the evaporation rate of the droplet. The flow rate of air, under all experimental conditions, was measured and these data were used to estimate the average velocity of air around the droplet. Experiments were also conducted on droplets of pure water and the results were compared. The initial mass fraction of urea, in the solution, did not appear to have a significant effect on the evaporation constant, but it did affect a few essential aspects of the evaporation behavior. The evaporation of water droplets was in accordance with the d2 law at all temperatures, whereas the evaporation of UWS droplets was ambient-temperature dependent. © 2019 American Institute of Chemical Engineers

AIChE Journal

Experimental investigation of the evaporation behavior of urea‐water‐solution droplets exposed to a hot air stream

The particle/droplet image analysis (PDIA) technique is often used for droplet sizing in sprays. Successful use of PDIA for drop size measurement in sprays mandates careful calibration and determination of the depth of field (DOF) for particles of different size classes. This is typically done with a calibration target that has circles etched on it. In the present study, a calibration experiment was performed with a calibration target as well as droplets, to evaluate the uncertainties in the measured sizes and also to compare the measured DOF values. A continuous-jet droplet generator was used to produce mono-disperse droplets of sizes ranging from 54-393 µm and the calibration glass plate used contained circles of sizes ranging from 20-400 µm. Images of these were captured using a CCD camera equipped with a long-distance microscope and were processed using a code written in MATLAB®. Differences in the measured sizes of droplets and circles and their DOF values are reported. It was observed that the use of the calibration target led to an underestimation of the error in droplet size measurements and an overestimation of the DOF. For the droplets, the measurement error was observed to be less than 5%, with the parameters chosen. © 2020 IOP Publishing Ltd.

Measurement Science and Technology

Estimation of measurement error and depth of field in PDIA experiments: a comparative study using water droplets and a calibration target

Autonomous robots in the real world should avert collisions with pedestrians and react quickly to sudden changes in the environment. Most local planners rely on static environment maps that cannot capture such critical elements of uncertainty. Learning based methods for end-to-end navigation have become popular recently, but it is still unclear how to incorporate collision avoidance in a simple, safe and quick manner. We propose a reinforcement learning curriculum based on domain randomization to train a high performing policy entirely in simulation. The policy is first trained in a simple obstacle-free environment to quickly learn point to point navigation. The learned policy is transferred to a dynamic environment to learn collision avoidance. The key idea is to randomize the obstacle dynamics to obtain a robust planner that can be directly deployed to the real world. The resultant policy outperforms conventional planners in dynamic real world environments, even when the robot is intentionally obstructed. © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2020.

Mechanisms and Machine Science

Crashing to Learn, Learning to Survive: Planning in Dynamic Environments via Domain Randomization

Electric discharge machining (EDM) is the most promising one to machine conductive materials irrespective of their hardness with good accuracy and precision. The plasma discharge phenomenon during EDM involves complex physics which needs to be understood. Several attempts are being tried by researchers in this direction but still, it required further efforts. The present study made to develop an FEA-based electrothermal model to simulate the temperature distribution and material removal rate in EDM of the aluminum alloy AA6061. The cylindrical disk-type heat source was assumed for the current model. To have more realistic machining conditions, the model has introduced a discharge current term in addition to discharge duration in defining the plasma radius and used the Gaussian heat flux. Also, both the conductive (due to plasma) and convective heat transfer (due to dielectric) modes were taken into consideration. The theoretical material removal rate (MRR) was estimated by assuming the cavity produced in the model as a hemispherical type. The EDM experimentation was performed on the AA6061 work material at similar electrical conditions used in the model. The experimental MRR was calculated from the weight difference (before and after machining) method. The results showed that the difference in theoretical (understated assumptions) and experimental MRR as 12%. The reasons for the MRR difference were also discussed in detail. © Springer Nature Singapore Pte Ltd. 2020.