K.R. Balasubramanian

Thermo-mechanical Analysis of TIG Welding of AISI 316LN Stainless Steel

In this research, thermoelastoplastic analysis using finite element modeling was carried out to study the thermomechanical behavior of 316LN stainless steel during autogenous tungsten inert gas welding. The efficiency of nondestructive testing was explored by validating the numerical simulations. Online temperature measurements were performed using infrared thermography. A detailed study of surface and bulk residual stress was performed using numerical modeling, and stress profiles were validated using X-ray diffraction and ultrasonic testing, respectively. Distortion analysis was validated using mechanical measurement. Nondestructive testing was efficiently used to validate the numerically predicted thermo-mechanical behavior of welded components.

Laser surface hardening: a review

Laser surface hardening (LSH) is one of the most widely used surface hardening process which can be applied to almost the whole range of metallic materials in today’s applications. Laser beam is focused to the localised region for hardening the required portion of the material. High intensity laser radiation is involved for heating the surface of steel into the austenitic region. Steep temperature gradient arises, due to high rates of heat transformation that results in instant cooling by conduction. It causes the phase conversion from austenite to martensite without the need for external quenching. Among various types of lasers, CO2, Nd: YAG and diode lasers are the widely used lasers for hardening in industries. This review paper is a summary of the basic fundamentals of laser hardening, figuring some of its benefits compared with conventional hardening technique. The works published by various researchers by experimentation and by numerical approach are presented.

Studies on biodiesel production and its effect on DI diesel engine performance, emission and combustion characteristics

Production of biodiesel from waste cooking oil was studied by experimental investigation using response surface methodology, specifically D-optimal design consisting of two levels. Waste cooking oil methyl ester (WCO-ME) produced under optimum transesterification process parameters was used in a direct injection diesel engine to evaluate the performance, emission and combustion characteristics at a constant speed of 1500 rpm. Results revealed that the biodiesel resulted in decreased brake thermal efficiency by 6% and higher brake-specific energy consumption of 25.9% when compared to diesel at 100% load condition. Carbon monoxide (CO), unburnt hydrocarbon, nitric oxide (NO) emission and smoke emission of WCO-ME decreased by 43.3%, 52.7%, 23% and 15.5%, respectively, compared to diesel. WCO-ME exhibited lower heat release rate, shorter ignition delay of 10.9°CA and slightly longer combustion duration of 54.4°CA when compared to diesel at same load condition.

Finite Element analysis of heat distribution in laser beam welding of AISI 304 Stainless Steel sheet

Laser beam welding of AISI 304 austenitic stainless steel is performed by varying beam power, welding speed, beam angle and gas flow rate to identify the influencing process parameters on weld bead geometry. Finite Element (FE) simulations are carried out using FE software SYSWELD considering the thermo-physical properties of the base material. A three-dimensional conical Gaussian heat source is employed for performing non-linear thermal analysis. The transient temperature profile and weld bead dimensions; depth of penetration and bead width are calculated by FE simulation. The simulated bead profile is compared with the experimentally measured profile and found to be very well correlated.

Optimization of activated tungsten inert gas welding of super duplex alloy 2507 based on experimental results

In this work, the effect of activated tungsten inert gas welding process parameters on the depth of penetration of super duplex stainless steel alloy 2507 has been analyzed using response surface methodology. The design matrix for conducting the experiments was generated using the central composite rotatable design of response surface methodology of design of experiments. The input process parameters like current, torch speed and arc gap were varied at five levels. Based on the generated design matrix, bead-on-plate welds were made on 10-mm-hick super duplex stainless steel plate. The depth of penetration, which is the response in the present analysis, was measured on the samples. A second-order response surface model was developed. Then, response optimization was performed for obtaining the maximum depth of penetration using desirability approach. The validation of the model showed good agreement between the predicted and actual values of depth of penetration.

Optimization of A-TIG welding of duplex stainless steel alloy 2205 based on response surface methodology and experimental validation

In the present work, optimum A-TIG welding process parameters have been determined using the design of experiments approach to achieve the desired depth of penetration (DOP) during welding of duplex stainless steel (DSS) alloy 2205. The design matrix for welding experiments was generated using the central composite design of response surface methodology. Bead-on-plate welds were made on 10 mm thick DSS alloy 2205 plates to generate data and to study the influence of process parameters on DOP. ANOVA analysis was carried out to determine the significance of the process parameters. Current was found to be a significant parameter influencing DOP. A second-order response surface model was developed to predict the response for the set of given input process parameters. Then, numerical and graphical optimization was performed to obtain the maximum DOP using desirability approach. Validation of the model showed good agreement between the predicted and actual values of DOP.

Finite Element Simulation of A-TIG Welding of Duplex Stainless Steel 2205 Using SYSWELD

Bead on plate activated tungsten inert gas (A-TIG) welding of duplex stainless steel (DSS) 2205 was performed to determine the thermal history, temperature distribution and the weld bead geometry. Finite element (FE) simulations were carried out using the software, SYSWELD considering the temperature dependent thermal and mechanical properties of the base material. A 3D double ellipsoidal heat source was employed for the non-linear thermal analysis. The transient temperature distribution, weld bead profile, weld bead dimensions, depth of penetration and bead width were calculated by FE simulation. The simulated weld bead profile was compared with the experimentally measured profile and found to be in agreement.

Dry sliding wear of laser hardened low alloy steel at room and elevated temperatures

This paper discusses about the wear behaviour of as-received and laser hardened EN25 low alloy steel performed in dry sliding condition using a pin-on-disc method. A 2 kW continuous wave neodymium yttrium-aluminium-garnet laser source is used for transformation hardening to improve the hardness and wear resistance. The laser transformation hardened steel samples are characterized by optical microscope, x-ray diffractometer and microhardness tester. The sliding wear study is conducted for different loads (10 N, 25 N, 40 N), sliding distances (1000 m, 2000 m, 3000 m) at various elevated temperatures (200℃, 400℃ and 600℃) with constant sliding speed of 0.15 m/s. The study at room temperature is also carried out for comparison. The friction and wear characteristics in sliding contact are evaluated and the worn surfaces are analysed through a scanning electron microscope. The experimental work indicates that wear resistance of laser hardened steel is five times higher than the as-received steel. The results also indicate that the wear resistance increases at 400℃ due to the oxide layer formation and decreases at 600℃ due to fracture of the oxide layer.

Mathematical modelling and optimisation of laser welding of butt joints

Laser welding is characterised by its high power density and concentrated heat input. The weld bead profile of laser welding depends on various parameters and these parameters are to be selected correctly to obtain the desired output. As the trial and error method for selecting weld parameters is very costly, suitable analytical methods has to be established for selecting optimum parameters for welding. In this paper the influence of laser welding parameters on the weld bead profile of butt joints are analysed and discussed. The experimentation is performed based on Box-Behnken design. Mathematical modelling is done to predict the responses and the adequacy of the model is tested using the analysis of variance. Numerical and graphical optimisation techniques are used to find the optimum process range which will improve the weld quality.

The Elevated Temperature Wear Analysis of Laser Surface–Hardened EN25 Steel Using Response Surface Methodology

The wear behavior of as-received and laser-hardened EN25 low-alloy steel is performed in dry sliding condition using a pin-on-disc-type machine. A response surface methodology–based Box-Behnken design is used to design the experimental matrix by reducing the number of experimental conditions and to develop mathematical models between the key process parameters. The process parameters considered are applied load, temperature, and sliding distance and the responses are wear rate and coefficient of friction. Analysis of variance is used to analyze the developed model. Laser surface–hardened samples exhibit a lower wear rate (0.099 × 103to 0.490 × 103mm3/m) and coefficient of friction (0.080 to 0.245 μ) compared to as-received samples.