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We report the applicability of the ultrafast pulse laser inscription technique to achieve high ablation depth on uncoated silicon wafer despite its higher surface reflectivity. The proposed methodology of this research work can be an alternative approach for the usual industrial practice of coating silicon surface with highly reflective materials for increasing the absorption phenomenon. To unveil the potential of the proposed methodology, a comparative study was carried out by fabricating microchannels of higher depth on uncoated and coated silicon wafer by varying repetition rate from 10 kHz to 500 kHz at a constant pulse energy of 18 μJ. The formation of ablation depth, ablation width and amorphous layer thickness was taken as the standard for evaluating the effectiveness of the proposed methodology. The experimental results revealed the formation of a higher ablation depth of 6.6 μm and an amorphous layer thickness of 0.039 μm for uncoated silicon material. Whereas, in the case of coated silicon material the ablation depth was found to be 3.199 μm with an amorphous layer thickness of 0.101 μm. This justified the applicability of the ultrafast pulse laser inscription technique for achieving quality microchannels having higher depth on silicon material without any surface coating. The underlying mechanism for the improved performance is due to the low temporal separation (μs) property of ultrafast lasers which results in negligible heat diffusion into the bulk material, thereby minimizing the collateral thermal damages. This was further proved based on an analytical model by evaluating the surface temperature at various repetition rates. The experimental and analytical results from the present work will be highly beneficial for the electronic industry, where the laser micro structuring of MEMS components made of silicon material is highly challenging due to its reflective property.

Die-sinking electrical discharge machining produces components with low repeatability as the process is inherently stochastic. Effects of its inputs and process parameters on the components’ dimensions are difficult to predict. This paper investigates the influence of input parameters like gap voltage, current, and pulse characteristics like percentage of “open”, “normal”, “arc” and “short” pulses on the dimensional features of the machined components. It discusses the methodology for extraction and estimation of amount of area machined, undercut and dimension by image processing. Support vector machine regression is applied to predict the dimension features based on the input and condition parameters.

The stochastic nature in the electrical discharge machining (EDM) is inherent to the process. The process instabilities like short-circuiting and arcing instances damage the workpiece and reduce machining efficiency. Pseudo-empirical or empirical relationships are presently in use for in-process control of parameters like discharge efficiency, energy consumption, and surface roughness. In this paper, a field-programmable gate array (FPGA)–based control strategy for discharge stabilisation is proposed, and a non-linear model for energy consumption is formulated to predict the in-process energy consumption. The model captures the dynamic behaviour of the EDM process. A novel method of pulse discrimination based on the pulse train gradient is used to determine the pulse duration, classify the pulses and finally calculate the discharge energy for building the model. A lumped control parameter named as gap condition number or “Gc number” is proposed to quantify the amount of debris and contaminants like soot and suspended particles in the electrode gap. Numerical simulations at various gap conditions and analysis for stability and sensitivity at different operating scenarios are studied. The simulation shows that the model converges to a single root for Gc number up to 1.93, undergoes periodic oscillations between two roots for the values between 1.93 and 2.42 and exhibits chaos for greater Gc numbers. Stability analysis of the model finds that the values of the non-dimensionalised discharge energy for which the energy oscillations during the discharge avoids arcing or short-circuiting are 60% of the maximum discharge energy. The present model has an increased monostability of 20% in comparison to a similar model and has a correlation of 63.48% with the experimental data. The proposed control strategy can be implemented to achieve stability control over the process, eventually improving the quality of machining.

In the work, the design and development of a novel Wire-EDM setup with double-wire guide discs is presented. It facilitates sparks to be generated between the workpiece and wire at two locations separated by the helical pitch distance. This sparking causes two helical grooves to be generated simultaneously on the surface of the workpiece when it is given suitable rotational speed and table feed. In this work, machining is carried out on rods of 1.5 mm diameter. Helical groves with helix angles ranging from 35 to 500 were generated and characterized. This method of machining the double helical grooves with a single pass reduces the machining time and eliminates the complexities involved in machining one groove at a time. It was observed that the proposed method is suitable for machining double helical grooves with helix angles in the range of 40 - 50°. The parts produced by the mentioned method can be used as EDM tools for generation of high aspect ratio holes in turbine blades and injection nozzles.

Surface texturing principle has already been reported to be successful in enhancing the tribological characteristics of various mechanical components including bearings, mechanical seal, piston rings, cylinder liner, etc. The current research work investigates the application of surface texturing principle on drill tools while machining titanium alloy. One of the major challenges pertaining to drilling of Ti-6Al-4V is the accumulation of heat at the machining zone due to the poor thermal conductivity property of the material. This factor deteriorates its applicability in various fields including aerospace, automobile, spacecraft, bio medical, etc. Accumulation of heat over the cutting regime will lead to rapid tool wear affecting the tool life and machined surface quality, which will eventually increase the total production cost. In drilling as the machining phenomenon occurs inside the hole, dissipation of accumulated heat is a real challenge. Moreover, the reachability of cutting fluids will get obstructed by the upward motion of chips along the helical groove. The above-mentioned challenge can be addressed by creating micro scale textures on drill tool surfaces, thereby controlling the heat generation by minimizing the sliding friction. Hence in the present work, micro scale textures in the form of circular dimples were created on the drill tool, and the same was coated for increasing the wear strength. Drilling experiments were performed under dry, wet and MQL conditions for evaluating the effectiveness of micro textured tools in cutting force reduction. From the experimental results, a net thrust force reduction of 13.83% in dry, 22.85% in wet and 21.65% in MQL condition were achieved while machining Ti-6Al-4V using coated flute and margin textured tool. Reduction in chip clogging phenomenon and lubrication enhancement provided by the coated micro scale textures are observed to be the underlying mechanism responsible for the lower cutting forces under all machining conditions.

Cooling holes in turbine blades made of high-temperature materials such Titanium alloys are produced by laser processing. A priori knowledge on laser interaction with material will be useful in the selection of laser parameters in practice. In the present work, two-temperature model consisting of a set of coupled Partial Differential Equations in spatial and time domain is used to study ultra-short pulse laser-matter interaction. The model is solved using finite element simulation available in COMSOL Multi-physics software. The present approach is validated taking gold as bench mark material as results for 1D and 2D cases are already reported in literature. The simulation approach is then extended to titanium alloy (Ti6Al4V), the material under investigation in our present work. The simulation results are obtained for 2.00 mm thick Ti6Al4V using 2D axi-symmetric two-temperature model. In order to compare the results, single-shot laser ablation experiments are carried out at laser fluency ranging from 0.84 to 8.4 Jcm−2. A method has been proposed in this work for assessing the crater depth and diameter uniquely from the images of the ablated specimens obtained using laser scanning confocal microscope. The simulation and experimental results are presented and discussed.

The real challenge pertaining to high aspect ratio drilling is the rapid increase in chip evacuation force due to the chip clogging phenomenon occurring at higher drilling depths. The clogged chips will further impede the reachability of cutting fluid at the machining zone leading to the tool temperature buildup. This will eventually result in the catastrophic failure of the tool. Hence, in the present work, an attempt has been made to minimize the chip evacuation force by functionalizing the drill tool surfaces based on the laser microtexturing principle. Microscale textures in the form of circular dimples were created on the flute and margin side of the drill tool with an objective to control the sliding friction, thereby minimizing the chip clogging effect. The effectiveness of the functionalized drill tools were assessed mainly based on the variation in thrust force and torque. Drilling experiments showed a net reduction of 17.18% in thrust force and 26.98% in torque while machining Ti–6Al–4V using the flute and margin textured tool, which justified the effectiveness of micro scale textures in minimizing the chip evacuation forces. The experimental analysis was further extended in terms of burr height evaluation, where FMT tools were found to be highly effective in burr height reduction (1.29 mm), showing a net reduction of 54.26% when compared with the non-textured tool. The outcomes from this research work will be highly beneficial for the manufacturing industries including aerospace, automobile, and spacecraft as high aspect ratio drilling of titanium alloys are still categorized to be the most challenging machining process owing to its lower thermal conductive property.

In metal cutting processes, reduction in sliding friction at the cutting regime can improve the machining performances in terms of cutting force reduction, built-up edge stabilization and improved surface integrity. However in drilling, as the cutting action occurs inside the hole, minimization of frictional effect at the contact interfaces is always a challenging task, as the reachability of cutting fluids at the machining zone is obstructed by the upward motion of chips sliding along the flute surface. This challenge can be addressed by functionalizing the drill tool surfaces with microtextures. Hence, in the present work, a novel drill tool having microtextures at the flute and margin side is used to reduce the sliding friction. The performance evaluation of microtextured drill tool was done based on the variation in thrust and torque. Margin textured tool was found to be more efficient than flute textured and non-textured tool recording a net thrust force reduction of 10–12% in dry, 15–20% in wet and 15–19% in MQL condition. Reduction in contact length, wear debris entrapment and formation of micropool lubrication effect at the cutting regime are found to be the underlying mechanisms responsible for the improved performance of microtextured drill tools.

The present work investigates the effectiveness of micro textures in reducing the sliding friction at the contact surfaces and its application on drill tools for the sustainable machining of Ti-6Al-4V. Preliminary experimental results from the pin on disc tests substantiated the tribology enhancing phenomenon of micro textured surfaces, with a better performance in case of micro dimpled surfaces recording a friction coefficient of 0.42. Hence for the first time, an attempt has been made to create micro textures on both the flute and margin side of the drill tools with an objective to minimize the cutting forces by reducing the sliding friction at the tool-chip and tool-work piece interfaces. Micro textures in the form of dimples were created on the flute and margin side of drill tool using laser micromachining technique. Drilling experiments were performed on Ti-6Al-4V work material by drilling a through hole of 10 mm depth using non-textured, flute textured and margin textured tools. From the cutting forces recorded during machining, it was observed that even at the higher cutting speed of 60 m/min and feed 0.07 mm/rev, the margin textured tool performed better than all other tool types recording a net reduction of 10.68% in thrust force and 12.33% in torque compared to non-textured tools. The investigations on the chip morphology further revealed less clogging of chips in case of flute textured tool which is a clear indication of a reduction in the chip evacuation force. The experimental results from this research work proved micro texturing of drill tool to be a viable technique for minimizing the energy loss due to reduction in frictional forces at the cutting regime while machining Ti-6Al-4V.

Wire electrical discharge turning (WEDT) process was developed to generate cylindrical form on any electrically conductive material applied in aerospace and automotive industry. The mechani...

Energy conservation is one of the most important aspects of electrical discharge machining process in which the material removal is by means of spark erosion. Metal removal in wire electrical discharge turning is a complex erosion mechanism which involves melting, vaporization and rapid cooling of molten material. In this work, the significance of discharge energy on the performance of wire electrical discharge turning process, namely, material removal rate, surface finish, thickness of recast layer and surface crack, is analyzed. New model to estimate material removal rate and surface finish in wire electrical discharge turning process have been proposed. Erosion energy and kinetic energy imparted by electrons and average physio-thermal properties of work material are utilized for the modeling. Proposed models are validated by conducting experiments on AISI 4340 steel material. The results obtained from the model are well in agreement with the experimental values. The influence of discharge energy on surface crack and recast layer thickness is analyzed using scanning electron microscope micrographs and energy-dispersive x-ray spectroscopy analysis. Surface crack is observed at higher discharge energy. The thickness of recast layer increases with the increase in discharge energy. Three-dimensional surface topography reveals the turbulent nature of machining process resulted from transient erosion phenomena of wire electrical discharge turning process. Higher material removal rates of the order of about 0.06 g/min with consistent average roughness in the range of 4.5–5.5 µm at the expense of 1.6–2.6 J of discharge energy are achieved in this work. The proposed models can be utilized for machining of difficult to machine material by effective utilization of energy that leads to energy conservation in wire electrical discharge turning process.

The demand for manufacturing axi-symmetric Ti-6Al-4V implants is increasing in biomedical applications and it involves micro turning process. To understand the micro turning process, in this work, a 3D finite element model has been developed for predicting the tool chip interface temperature, cutting, thrust and axial forces. Strain gradient effect has been included in the Johnson–Cook material model to represent the flow stress of the work material. To verify the simulation results, experiments have been conducted at four different feed rates and at three different cutting speeds. Since titanium alloy has low Young’s modulus, spring back effect is predominant for higher edge radius coated carbide tool which leads to the increase in the forces. Whereas, polycrystalline diamond (PCD) tool has smaller edge radius that leads to lesser forces and decrease in tool chip interface temperature due to high thermal conductivity. Tool chip interface temperature increases by increasing the cutting speed, however the increase is less for PCD tool as compared to the coated carbide tool. When uncut chip thickness decreases, there is an increase in specific cutting energy due to material strengthening effects. Surface roughness is higher for coated carbide tool due to ploughing effect when compared with PCD tool. The average prediction error of finite element model for cutting and thrust forces are 11.45 and 14.87 % respectively.

Micro-electrical discharge machining is a stochastic process where the interaction between the materials and the process parameters are difficult to understand. Monitoring of the process becomes necessary to achieve the dimensional accuracy of the micro-featured components. Although thermo-mechanical erosion is the most accepted material-removal mechanism, it fails to explain the material removal with very short pulse duration. Alternative postulate like electrostatic force-induced stress yielding provides a stronger argument, rising ambiguity over the material-removal process in the micro-electrical discharge machining regime. In this work, it was found that the stress waves released from the material during micro-electrical discharge-machining process indicate material removal by mechanical deformation and fracture mechanism. These stress waves were captured using the acoustic emission sensor. The discharge pulses were captured by voltage measurement and classified using voltage gradient and machining time duration into three major categories, open pulse, normal pulse and arc pulse. The acoustic emission signal features were extracted and identified by time–frequency–energy distribution analysis. A feed-forward back-propagation neural network mapping of the pulse instances was performed with the obtained acoustic emission signature. The time–frequency–energy distribution analysis of the acoustic emission and the scanning electron microscope images of the craters provide conclusive evidence that the material is removed by mechanical stress and fracture. The feed-forward back-propagation network model was trained to predict the discharge categories of the pulse instances with AE signal inputs which can be used for monitoring the material-removal mechanism in micro-electrical discharge machining operation.

Silicon material has been extensively used in electronics, optoelectronics, and Microelectromechanical Systems (MEMS). In spite of good mechanical behavior exhibited by the silicon material, their brittleness causes difficulty in machining, which greatly affects the surface integrity of the machined parts. This demands a need for further investigations in this area for improving the material removal rate and surface integrity. Ultrashort-pulsed laser machining techniques have brought new perspectives for efficient machining of semiconductor materials in terms of surface integrity and energy consumption. In the present work, the effect of number of pulses and repetition rate at 1064 and 532 nm wavelengths of a picosecond laser has been investigated for dimensional quality and subsurface defects of holes. Further experiments were conducted using a femtosecond laser to understand the effect of repetition rate, pulse duration, pulse energy, and scanning speed on the quality of kerf surface.