Summary of the Publications

JOURNALS

1) Multiphysics modelling and high-speed imaging-based validation of discharge plasma in micro-EDM, CIRP Journal of Manufacturing Science and Technology, Volume 43, 2023, Pages 15-29, https://doi.org/10.1016/j.cirpj.2023.02.006.

Authors: Sohaib Raza, Hreetabh Kishore, Chandrakant Kumar Nirala, K.P. Rajurkar

This paper describes the plasma channel formation during the micro-electrical discharge machining (micro-EDM) at various voltage and capacitance settings. A numerical model using COMSOL Multiphysics finite element is developed to estimate the plasma parameters, such as the plasma channel diameter and temperature distribution in the radial and axial directions. The numerical model also predicts the heat flux distribution responsible for material melting and subsequent removal. Additionally, the coupled numerical model explains the plasma-electrode interactions via different heat transfer mechanisms such as conduction, convection, radiation and thermionic effect. Experimental plasma diameters obtained from high-speed imaging of the discharge process were compared with the simulation results and were in close agreement, with an error between 5% and 14.5%. The simulated molten diameters at various input parameters were compared with experimental crater diameters of single craters and observed to follow a similar trend.

2) Performance Measurement And Discharge Data Based Analysis Of Ultrasonic Assisted µEDM For Ti6Al4V, ASME. J. Micro Nano-Manuf. (2023). doi: https://doi.org/10.1115/1.4062819.

Authors: Sohaib Raza ., Airao, J., and Nirala, C. K

Unconventional machining of difficult-to-cut conductive materials with high accuracy, low heat-affected zone formation and the ability to cut intricate geometries entitles Micro-electrical discharge machining (µEDM) as the most versatile technology in micromachining. Ultrasonic vibration assistance further enhances the material-removing ability of the µEDM process while imparting several other benefits. The present work proposes a comparative study between the unassisted and ultrasonic vibration assisted µEDM to the tool electrode for machining micro slots on Ti6Al4V material using an in-house developed tool holder. The characteristics of the discharge waveforms were captured using a data acquisition system at high sampling rates. The pulse discrimination system is used to perform an in-depth study of the discharge pulses. µEDM milling experiments were performed to machine micro slots at varying input voltages, capacitances and feed rates. The ultrasonic vibrations proved beneficial in addressing the primary issue associated with the µEDM process, i.e. the material removal rate (MRR) with a maximum of 35% increment. Applying ultrasonic vibrations reduced the recast layer and tool wear rate (TWR) and increased the surface finish.

3) Real-time data acquisition and discharge pulse analysis in controlled RC circuit based Micro-EDM. Microsystem Technologies, (2023). https://doi.org/10.1007/s00542-023-05432-x.

Authors: Sohaib Raza ., Nadda, R. & Nirala, C.K.

Owing to the non-isoenergetic discharge pulses in an RC-based micro-electrical discharge machining (µEDM) process, the unit material removal analysis is difficult. It requires a robust discharge pulse acquisition and monitoring system to capture, process and record live discharge data. Effective acquisition and monitoring of discharge pulses need an experimental diagnosis in real-time. The present work proposes a technology to monitor the discharge pulses of a controlled RC-based µEDM in real-time. Signals, while being acquired through various sensors, are processed in NI LABVIEW-based data acquisition (DAQ) system. Extensive virtual instrumentation is performed to categorize the discharge pulses in contributing, semi-contributing and non-contributing towards material removal, through an in-house developed pulse discrimination system (PDS). The developed PDS is simultaneously used to estimate the real-time discharge energies of individual pulses and their histograms with the machining progress. The acquired information from the developed PDS is used to justify the variations in discharge energy, material removal, and tool wear, with increasing machining depth. The PDS has shown the potential of predicting the conventionally unpredictable real-time unit volume removal during the process, which may be considered an important tool to meet the current industrial demands for remote access and monitoring of the process.

4) Multiphysics simulation of plasma channel formation during micro-electrical discharge machining", AIP Advances 11, 025138 (2021) https://doi.org/10.1063/5.0028665.

Authors: Sohaib Raza and Chandrakant Kumar Nirala

A 2D axisymmetric plasma model for micro-electrical discharge machining (μEDM) is developed, and the discharge phenomenon is discussed in this paper. Variations in different plasma properties, such as density, temperature, and collisions of the electrons bombarding the anode and cathode electrodes, were simulated to comprehensively explain the discharge process. The said properties of the plasma channel will be extremely helpful in determining the heat flux available at the tool and workpiece of μEDM. The governing equations of electrostatics, drift-diffusion, and heavy species transport were coupled together and solved simultaneously for computing the properties of the plasma channel in water vapor. The simulation describes the movement of electrons and ions in the inter-electrode gap during the discharge initiation under the applied electric field. The anode spot responsible for the material removal was formed much earlier compared to the cathode spot formed at the tool. A clear difference in the density as well as temperature of the electrons was observed between the work piece and the tool surface with the former being at the higher side in both the cases. The temperature of the electrons and the current density of the plasma obtained during the simulation will be useful to determine the heat flux responsible for the material removal. The higher density of the electrons at the anode was responsible for more collisional power loss and higher capacitive power deposition.

5) Sensors-based discharge data acquisition and response measurement in ultrasonic assisted micro-EDM drilling, Measurement: Sensors, Volume 29, 2023, 100858, ISSN 2665-9174, https://doi.org/10.1016/j.measen.2023.100858.

Authors: Sohaib Raza, Rahul Nadda, Chandrakant Kumar Nirala

Micro-electrical discharge machining (μEDM) suffers from the problem of low material removal rate (MRR) and poor surface finish, especially when there are recurring abnormal sparks. Such sparks are mainly due to the accumulation of unflushed debris in the discharge zone resulting in a frequent arcing phenomenon. Vibration assistance to μEDM has proven contributions to the MRR and surface finish enhancement, but the intrinsic information on discharge pulse modification due to the vibration is unclear. The present work proposes a pulse categorization strategy to understand the nature of discharge pulses during the conventional and ultrasonic vibration assisted μEDM. The discharge pulses were acquired at a sufficiently high sampling rate using NI LABVIEW-based data acquisition through an in-house developed pulse discrimination system (PDS). The developed PDS is simultaneously used to estimate the real-time discharge energies of individual pulses and their histograms with the machining progress. The acquired information from the developed PDS is used to justify the variations in discharge energy, discharge frequency, surface roughness and accuracy with increasing machining depth. Vibration assistance to the μEDM process was found beneficial, with an 18% increase in the discharge energy, and a 7.14% reduction in the percentage error in depth. The surface roughness at high-energy settings reduces from 3.2 μm to 0.45 μm because of ultrasonic vibration assistance.

6) Discharge Pulse Analysis Based Machining Responses in Vibration Assisted µEDM Processes. MAPAN 37, 777–792 (2022). https://doi.org/10.1007/s12647-022-00591-0.

Authors: Sohaib Raza ., Nadda, R. & Nirala, C.K.

The frequent occurrence of inherent abnormal discharges with the progress of machining in resistance–capacitance (RC) based micro-electrical discharge machining (µEDM) affects the product quality and material removal rate (MRR). This work presents a data acquisition-based analysis to address these alterations by exploring the nature of discharge pulses of vibration-assisted µEDM process variants. A cost-effective vibrating spindle attachment is developed for preliminary testing of vibration assistance to the controlled RC-based µEDM and reverse-µEDM processes. Micro-grooves of 5 mm x 500 µm × 500 µm and arrayed micro-rods with an aspect ratio of 20 with a diameter of 0.1 mm were fabricated using µED-milling and reverse-µEDM, respectively. Two different frequencies, 100 and 150 Hz, are used in vibration-assisted machining, leading to a maximum 57% reduction in machining time. The discharge pulses acquired during the machining showed a significant decrease in the arcing phenomenon that helps to understand the variation in MRR, surface finish, and overcut.

7) Analysis of Discharge Gap using Controlled RC based Circuit in µEDM Process. J. Inst. Eng. India Ser. C 103, 21–27 (2022). https://doi.org/10.1007/s40032-021-00711-w.

Authors: Sohaib Raza , Nadda, R. & Nirala, C.K

Owing to the dependency of real-time inter-electrode gap (discharge gap) on instantaneous discharge voltage in a resistance–capacitance (RC) circuit-based µEDM, analyzing machining responses with respect to the discharge gap could be a crucial task. This work aims to extract the information on the material removal rate (MRR) and overcut at various discharge gaps, set in terms of open-circuit voltage in a controlled RC-based µEDM setup. The results have been obtained for MRR and overcut and found to be in good agreement with logical reasoning. The results have been further supported by a thorough discussion in the context of the discharge gap and corresponding discharge energy. A DAQ system has been used to capture the real-time discharge voltage data and corresponding amperage at a high sampling rate to estimate the discharge energy.

8)  Comparative analysis of single-crater parameters in ultrasonic-assisted and unassisted micro-EDM of Ti6Al4V using discharge plasma imaging;. Nanotechnol. Precis. Eng., 1 May 2024; 7 (2): 023002. https://doi.org/10.1063/10.0023965

Authors: Sohaib Raza and Chandrakant Nirala

Ultrasonic-assisted micro-electro-discharge machining (μEDM) has the potential to enhance processing responses such as material removal rate (MRR) and surface finish. To understand the reasons for this enhancement, the physical mechanisms responsible for the individual discharges and the craters that they form need to be explored. This work examines features of craters formed by single discharges at various parameter values in both conventional and ultrasonic-assisted μEDM of Ti6Al4V. High-speed imaging of the plasma channel is performed, and data on the individual discharges are captured in real-time. A 2D axisymmetric model using finite element software is established to model crater formation. On the basis of simulation and experimental results, a comparative study is then carried out to examine the effects of ultrasonic vibrational assistance on crater geometry. For every set of μEDM parameters, the crater diameter and depth from a single discharge are found to be higher in ultrasonic-assisted μEDM than in conventional μEDM. The improved crater geometry and the reduced bulge formation at the crater edges are attributed to the increased melt pool velocity and temperature predicted by the model.

CONFERENCES