Souren Mitra

Optimization of Nd:YAG Laser Parameters for Microdrilling of Alumina with Multiquality Characteristics via Grey–Taguchi Method

In laser microdrilling, the formation of taper and the dimension of the heat-affected zone (HAZ) are important attributes that greatly influence the quality of a drilled hole. In this article, an experimental investigation into Nd:YAG laser microdrilling of alumina is carried out to produce desired high-quality microdrill. Four independently controllable process variables viz. lamp current, pulse frequency, air pressure, and pulse width are considered as input parameters, while hole taper and HAZ width are considered the output parameters. The Taguchi method combined with the grey relational analysis is used as a statistical design of experiment technique to set the optimal process parameters. The objective is set to minimize both quality characteristics, simultaneously. Grey relational analysis is applied to convert the multiple quality characteristics to a single performance characteristic, called grey relational grade. Optimal process parameters are then determined by the Taguchi method using grey relational grade as the quality index. Both of the quality characteristics of drilled holes are improved markedly at the optimal process condition, as verified by an additional confirmation test. This indicates the application feasibility of the grey-based Taguchi technique for continuous improvement of laser microdrilling quality in the manufacturing industry.

An Integrated Approach to Optimization of WEDM Combining Single-Pass and Multipass Cutting Operation

This research article presents an integrated approach to optimization of wire electrical discharge machining (WEDM) of gamma titanium aluminide (γ-TiAl) with the assistance of artificial neural network (ANN) modeling. Four process parameters, pulse on time, peak current, dielectric flow rate, and effective wire offset, were investigated to study their influence on the process outputs; that is, cutting speed, surface roughness, and dimensional shift in the multipass cutting operation. Two ANN models, based on Bayesian (automated) regularization and early stopping method, have been developed and compared. The model based on Bayesian regularization method was selected because the prediction accuracy was superior compared to the early stopping method. The Pareto optimization was applied to determine the maximum cutting speed corresponding to the required surface roughness for the trim cutting process. Finally, by combining the results of the single- and multipass cutting and introducing the new concept of effective cutting speed, a machining strategy based on the novel concept of critical surface roughness has been developed for selecting the machining process, either single cutting or multipass cutting, so that the maximum productivity can be ensured according to the surface finish requirements.

Electro Discharge Machining of Titanium Nitride-Aluminium Oxide Composite for Optimum Process Criterial Yield

Titanium nitride-aluminium oxide (TiN–Al2O3) is a new generation ceramic composite material having potential for many industrial applications as it possesses high resistance to thermal degradation, anti-wear and anti-abrasion properties. But conventional machining of such ceramic composite is difficult to perform for some of its peculiar properties like anisotropy, low thermal conductivity, and abrasive nature of the reinforcing phases. In the present investigation, non-conventional machining like electro discharge machining (EDM) has been carried out to machine the material. Energy dispersive X-ray spectroscopy and X-ray diffraction analysis have also been carried out on the composite matrix to verify the presence of two distinguishable phases of TiN and Al2O3. The present article reports the effects of EDM process parameters on material removal rate, electrode wear rate, radial overcut, and taper angle while machining TiN–Al2O3 composite. The characteristic features of the EDM process are explored through Taguchi L9 orthogonal array design–based experimental studies with various process parametric combinations. Finally, optimum parameter settings for each response factor are obtained and tested through verification experiments. The whole experimental study indicates that EDM has a very good potential in machining of TiN–Al2O3 ceramic composite in some particular ranges of process parameters.

Multi criteria FMECA for coal-fired thermal power plants using COPRAS-G

Purpose – The purpose of this paper is to present a multi criterion failure mode effect and criticality analysis for coal-fired thermal power plants using uncertain data as well as substituting the traditional risk priority number estimation method. Design/methodology/approach – Grey-complex proportional assessment (COPRAS-G) method, a multi criteria decision making tool is applied to evaluate the criticalities of the failure modes (alternatives). In this model the criteria (criticality factor) against each alternative are expressed in grey number instead of crisp values. Findings – Rupture failure of the straight tube of economizer (ECO) due to erosion is the highest critical failure mode whereas rupture failure of the stub of ECO due to welding defect is the lowest critical failure mode. Originality/value – This paper incorporates human and environmental factors as additional factors which also influence the failure modes significantly. The COPRAS-G method is modified according this problem. Uncertainty...

Effects of Process Parameters on Hole Circularity and Taper in Pulsed Nd:YAG Laser Microdrilling of Tin-Al2O3 Composites

This study investigates the effect of five parameters on circularity and taper of drilled holes in pulsed Nd:YAG laser microdrilling process. The effect of various process parameters like lamp current, pulse frequency, pulse width, air pressure, and focal length of Nd:YAG laser microdrilling on hole circularity at entry, exit, and taper has been investigated through response surface methodology (RSM)–based experimental study. The significant parameters have been selected based on the analysis of variance (ANOVA). The parametric combination for optimal hole circularity and hole taper has also been evaluated. In micromanufacturing, circularity of a drilled hole at entry, exit, and taper are important attributes which greatly influence the quality of a drilled hole. The drilling operation has been carried out on titanium nitride-alumina (TiN-Al2O3) composite, an important electroconductive ceramic suitable for wear and heating applications.

An experimental investigation on Nd:YAG laser microchanneling on polymethyl methacrylate submerged in water:

In this research work, an experimental investigation has been carried out on underwater laser microchanneling on polymethyl methacrylate, using a pulsed Nd:YAG laser system. The underwater laser processing has been used to minimize the heat-affected zone, microcracking and burr formation around the microchannel. The process parameters that have been taken into consideration are lamp current, pulse frequency, pulse width and cutting speed. The microchannel characteristics that have been taken into account as responses are microchannel width, microchannel depth, burr width and burr height. Response surface methodology has been used to develop the mathematical relationships between the process parameters and microchannel characteristics. The adequacies of the models have been tested using analysis of variance. The interaction effects of process parameters on the microchannel characteristics have been analyzed and discussed. In addition to that, single-objective and multiobjective optimization of the process parameters have been performed to obtain desired values of microchannel characteristics.

Selection of Process Parameters for Optimizing the Weld Strength in Laser Transmission Welding of Acrylics

In this paper, an experimental investigation into laser transmission welding of acrylics is carried out. The Taguchi method of parameter design is used as a statistical design of experiment technique to set the optimal process parameters. Experiments are designed and conducted by using Taguchis L16 orthogonal array. Maximization of weld strength is selected as the quality target. The signal-to-noise ratio and the analysis of variance are used to find the optimum levels within the window of parameters selected and to identify the order of importance of the process parameters. With the frame of this work the effects of process parameters on weld strength is also discussed. Finally, a confirmation test is conducted, which verifies that optimal laser transmission welding parameters can be determined effectively so as to improve weld strength through the Taguchi method.

Experimental investigation and multi-objective optimization of wire electrical discharge machining (WEDM) of 5083 aluminum alloy

Abstract The experimental analysis presented aims at the selection of the most optimal machining parameter combination for wire electrical discharge machining (WEDM) of 5083 aluminum alloy. Based on the Taguchi experimental design (L9 orthogonal array) method, a series of experiments were performed by considering pulse-on time, pulse-off time, peak current and wire tension as input parameters. The surface roughness and cutting speed were considered responses. Based on the signal-to-noise (S/N) ratio, the influence of the input parameters on the responses was determined. The optimal machining parameters setting for the maximum cutting speed and minimum surface roughness were found using Taguchi methodology. Then, additive model was employed for prediction of all (3 4 ) possible machining combinations. Finally, a handy technology table has been reported using Pareto optimality approach.

Experimental investigation on die corner accuracy for wire electrical discharge machining of Monel 400 alloy

The experimental research presented in this article explores the wire electrical discharge machining of Monel 400 alloy. An L-18 orthogonal array has been used for experimentation by considering machine controllable factors (i.e. wire tension, pulse-on time, pulse frequency, peak current and servo voltage) and machine uncontrollable factors (namely flushing nozzle height, workpiece thickness and corner angle) as process parameters. Using Taguchi methodology, the influence of the process parameters on the responses, such as material removal rate, surface roughness and corner error, were studied. The impact of pulse parameters modification in corner accuracy improvement has been analyzed. Finally, using Taguchi’s additive model predictions and Pareto optimality approach, a sample technology table for a specific machining condition has been reported for ready use.

Availability and cost-centered preventive maintenance scheduling of continuous operating series systems using multi-objective genetic algorithm: A case study

Abstract This article presents a multi-objective (maximization of availability and minimization of maintenance cost) preventive maintenance (PM) scheduling model for a continuous operating series system (COSS) which do not provide an off-working period for PM. The objective functions are optimized by using a Multi-Objective Genetic Algorithm (MOGA). The effectiveness of the model is demonstrated through a coal-fired boiler-tube. The case study shows that the model can improve the availability along with profound reduction of the maintenance cost, i.e., increases the profit of the plant.