Shrikrishna N. Joshi

Intelligent process modeling and optimization of die-sinking electric discharge machining

This paper reports an intelligent approach for process modeling and optimization of electric discharge machining (EDM). Physics based process modeling using finite element method (FEM) has been integrated with the soft computing techniques like artificial neural networks (ANN) and genetic algorithm (GA) to improve prediction accuracy of the model with less dependency on the experimental data. A two-dimensional axi-symmetric numerical (FEM) model of single spark EDM process has been developed based on more realistic assumptions such as Gaussian distribution of heat flux, time and energy dependent spark radius, etc. to predict the shape of crater, material removal rate (MRR) and tool wear rate (TWR). The model is validated using the reported analytical and experimental results. A comprehensive ANN based process model is proposed to establish relation between input process conditions (current, discharge voltage, duty cycle and discharge duration) and the process responses (crater size, MRR and TWR) .The ANN model was trained, tested and tuned by using the data generated from the numerical (FEM) model. It was found to accurately predict EDM process responses for chosen process conditions. The developed ANN process model was used in conjunction with the evolutionary non-dominated sorting genetic algorithm II (NSGA-II) to select optimal process parameters for roughing and finishing operations of EDM. Experimental studies were carried out to verify the process performance for the optimum machining conditions suggested by our approach. The proposed integrated (FEM-ANN-GA) approach was found efficient and robust as the suggested optimum process parameters were found to give the expected optimum performance of the EDM process.

Finite element simulation of laser assisted bending with moving mechanical load

Laser bending is an advanced technique to bend the sheet metal worksheet by means of thermal stresses instead of mechanical forces. It is a non-contact type process in which a concentrated high power laser beam works as a processing tool. In the present work, three-dimensional sequential thermo-mechanical non-linear elasto-plastic numerical model of laser-assisted bending has been developed by using finite element method. The developed numerical model is used to analyse laser bending of magnesium alloy AZ31B worksheet with a moving mechanical load. The effects of transient load on stress-strain distribution and bend angle distribution in the sheet metal worksheet are investigated. The results showed that the bending of worksheet depends on the laser beam parameters as well as magnitude of mechanical load applied. These results will be useful in the precision bending of difficult-to-form materials using laser bending process.

Numerical modeling and experimental validation of curvilinear laser bending of magnesium alloy sheets

Laser bending is an innovative technique to obtain the required bend-angle and sheet metal curvature by means of laser beam irradiation with controlled laser parameters. In this work, a numerical investigation on curvilinear laser bending of magnesium M1A aoy sheets has been carried out. Three-dimensional sequential transient thermomechanical numerical model is developed by using finite element method. The model has been validated by comparing the predicted results with those obtained in the experiments. The curvilinear laser bending process is studied in terms of temperature distribution, stress–strain distribution, bend angle and displacement at the edges. The results showed that the bend angle increases with increase in scanning path curvature. It is observed that the displacement at various edges and final shape of the worksheet are affected by the scanning path curvature. The results will be useful in adjustment and alignment processes and the generation of complex shapes using lasers.

Three-dimensional numerical modeling, simulation and experimental validation of milling of a thin-wall component

Study on mechanics of milling of thin-wall components using a helical end mill is important in view of its complex nature and prominent applications in aerospace, automobile and electronics areas. This article presents a realistic three-dimensional, thermo-structural, finite-element-based mathematical model for thin-wall milling of aerospace grade aluminum alloy. Lagrangian formulation with explicit solution scheme was employed to simulate the interaction between helical milling cutter and the workpiece. Behavior of the material at high strain, strain rate and temperature was defined by Johnson–Cook material constitutive model. Johnson–Cook damage law and friction law were used to account for chip separation and contact interaction. Experimental work was carried out to validate the results predicted by the mathematical model. The developed model predicted the forces in radial, feed and axial directions with errors of 14%, 26% and 33%, respectively. The prediction errors for deflections at top, middle and bottom portions of thin wall were within 11%–39%. The simulated chip dimensions were in good agreement with experimental results while the computed cutting temperature varied by 17% with respect to the experimental value. Overall, it was found that the developed model predicts the process responses with fair and acceptable prediction accuracy. Using the developed model, a study on the effect of process parameters on the performance parameters, namely cutting and thrust forces, stress distribution, cutting temperature, part deflection and chip morphology was carried out, which is not possible using a two-dimensional orthogonal or oblique cutting model. It was found that the developed three-dimensional mathematical model provided very useful insights into the complex physical interaction of helical cutting tool and workpiece during thin-wall milling of aerospace alloys.

Bioinspired Composite Materials: Applications in Diagnostics and Therapeutics

Evolution-optimized specimens from nature with inimitable properties, and unique structure–function relationships have long served as a source of inspiration for researchers all over the world. For instance, the micro/nanostructured patterns of lotus-leaf and gecko feet helps in self-cleaning, and adhesion, respectively. Such unique properties shown by creatures are results of billions of years of adaptive transformation, that have been mimicked by applying both science and engineering concepts to design bioinspired materials. Various bioinspired composite materials have been developed based on biomimetic principles. This review presents the latest developments in bioinspired materials under various categories with emphasis on diagnostic and therapeutic applications.

Comparison of the Performance of Lubricants in Rolling Based on Temperature Measurement

Lubricants are used in rolling process mainly to reduce the friction. Thus, the measurement of friction can give the idea about the performance of a lubricant. However, the measurement of friction by no means is an easy task. In the past, various methods have been employed for measuring the friction in rolling. Some of these methods require damaging of the surface of the rolls. The methods based on the measurement of roll force, roll torque and the slip can be easily used, but their reliability is dependent on reliability of measuring devices and the mathematical model. A possible way of measuring the average coefficient of friction in rolling is to measure the exit temperature of the strip. It can be easily done by means of temperature sensors. In this work, an inverse method of estimating the approximate value of friction coefficient is proposed based on the exit temperature measurement. The inverse model makes use of a direct model of temperature determination, which is based on finite element analysis and analytical models available in the literature. For a given exit temperature, the inverse model searches the appropriate value of friction coefficient using golden section search algorithm. The methodology is tested by carrying out a number of numerical experiments on the cold strip rolling. Some preliminary experiments have been conducted. It is planned to carry out more experiments in future. Although the direct model used in this work is highly approximate, the entire methodology displays its high potentiality in an industrial setting. In any case, the methodology can compare two lubricants with respect to their ability to reduce the coefficient of friction, even if the estimated coefficient of friction may be approximate.

Optimum process parameters for efficient and quality thin wall machining using firefly algorithm

The manufacturing requirements of the aerospace industry makes it imperative to use thin wall machining techniques to machine parts that would otherwise have to be assembled from a number of parts. To achieve high productivity, there must be increase in material removal rate, which is constrained by the geometrical accuracy and surface finish requirements. Thus, a compromise must be made between productivity and product quality. This paper presents an optimisation scheme to improve the productivity while keeping the surface finish within acceptable limits during thin-wall machining operations. Initially full factorial experiments were carried out on machining of closed thin walled pocket by varying feed, cutting speed and tool diameter. Surface roughness and material removal values for all experiments were recorded. Analysis of variance was carried out to find out the most significant process parameter. Later firefly algorithm, a nature inspired swarm optimisation technique was employed to obtain the optimum process parameters for desired performance. A confirmation experiment was carried out which indicates an error of 1.27% and 1.03% between predicted and experimental results of surface roughness and material removal rate respectively.

Research issues in the laser sheet bending process

Abstract Laser sheet bending is a process in which a laser source heats up the material in order to induce thermal stresses sufficient enough to cause bending. A slight variant of the process is laser-assisted bending, where both a mechanical load and laser heat source are employed for bending. Three different mechanisms (either separately or in combination) are active in laser bending. These are the temperature gradient mechanism, buckling mechanism, and upsetting mechanism. Laser bending has several advantages compared to mechanical bending, but has some limitations, too. The important process parameters are laser power, scan speed, beam diameter, absorption coefficient, number of passes, and cooling conditions. The workpiece material and worksheet geometry also affect the process. There have been some studies on microstructural and mechanical properties of laser bent sheets. In general, the findings are encouraging and suggest that the product quality is not deteriorated in comparison to mechanical bending. Attempts have also been made to carry out curvilinear laser bending and producing various forms on the sheets. The mathematical modeling of the process, inverse modeling, optimization, and control are hot research areas along with experimental research. It is envisaged that research and applications in the area of laser bending will be strengthened in the near future.

A Numerical Investigation into the Effect of Forced Convection Cooling on the Performance of Multi-scan Laser Bending Process

Laser bending is a process of deforming metal worksheets using thermal stressed generated due to controlled laser heating of work material. It can produce precise bend angle in the worksheet. This chapter presents 3D nonlinear transient thermomechanical numerical modeling and simulation of forced air cooling of laser bending process. Simulations have been carried out by using finite element method (FEM). Parametric study on the variation of important process parameters, viz., laser power, scan speed, number of scans on the stress–strain distribution, temperature distribution, bend angle and edge effect is studied. The results of forced cooling are compared with those of natural cooling. The results showed a significant improvement in the performance of multi-scan laser bending process with the application of forced cooling.

Numerical Modeling and Experimental Validation of Machining of Low-Rigidity Thin-Wall Parts

In the present work, a realistic three-dimensional thermomechanical finite element method (FEM) based model is developed to simulate the complex physical interaction of helical cutting tool and workpiece during thin-wall milling of an aerospace grade aluminum alloy. Lagrangian formulation with explicit solution scheme is employed to simulate the interaction between helical milling cutter and the workpiece. The behavior of the material at high strain, strain rate, and the temperature is defined by Johnson–Cook material constitutive model. Johnson–Cook damage law and friction law are used to account for chip separation and contact interaction. Experiments are carried out to validate the results predicted by the developed 3-D numerical model. Four case studies are conducted to test the capability of developed 3-D numerical model. It is noted that the milling force and wall deformation predicted by the developed model match well with the experimental results. Overall, this work provides a useful tool for prior study of the precision machining of low-rigidity thin-wall parts.