G. Buvanashekaran

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.

Feasibility of Magnetically Impelled Arc Butt (MIAB) Welding of High-Thickness Tubes for Pressure Parts

Magnetically impelled arc butt (MIAB) welding is a solid phase pressure welding process similar to flash-butt welding, but it uses a magnetic field to rapidly spin the arc. The spinning arc provides a more consistent interior and exterior weld flash than typically seen on the flash-butt upset areas. MIAB welding process is presently being employed for welding tubular sections in automobile industries in various parts of United Kingdom and Germany. However, there are no details reported in available literatures on application of MIAB welding process for pressure parts. Hence, in this study, a pivotal attempt is being made to employ MIAB welding process to weld carbon steel tubes (51 mm and 44 mm outer diameter) and (5-6 mm thick) in economizer coils of pressure vessel. Several trials are conducted to create an optimal parameter window for MIAB welding process by varying the different input parameters. Further, mechanical testing and metallurgical characterization are carried out on the MIAB-welded specimen to evaluate its strength and to assess the weld integrity. The results of the experiment emphasized that the MIAB-welded joints exhibited high strength and good weld integrity.

Magnetic flux distribution modelling of magnetically-impelled arc butt-welding of steel tubes using finite-element analysis

Magnetically-impelled arc butt-welding (MIAB) is a pressure-welding process. In this process, heat is generated prior to forging by an arc created between two clamped and aligned tubes. This arc rapidly rotates along the peripheral edges of the tubes to be welded due to the electromagnetic force resulting from the interaction of the arc current and the magnetic field in the gap. To be precise, the magnetic flux density is the significant parameter that governs the arc rotation and the weld quality. This paper presents a three-dimensional finite-element model to determine the magnetic flux density distribution in the MIAB welding process. The objective of this study is to perform a non-linear electromagnetic analysis using the finite-element package ANSYS, and to explore the interdependence of MIAB welding parameters such as gap size, exciting current in the coil, and coil position from the weld centre, which influence the electromagnetic force generated in the welding process and weld quality. The results of this analysis are verified with the available experimental data for steel tubes (outer diameter 50 mm and thickness 2 mm). The results obtained using finite-element analysis establish that the magnetic flux density distribution in the gap increases with increasing exciting current and decreasing gap size and coil position from the weld centre.

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.

Simulation of Magnetic Flux Distribution for Magnetically Impelled Arc Butt Welding of Steel Tubes

This paper proposes a 3‐Dimensional Finite Element Model (FEM) for the simulation of magnetic flux distribution in a Magnetically Impelled Arc Butt (MIAB) welding process. The electromagnetic force responsible for the arc rotation in MIAB welding process is governed by the magnetic flux density in the gap, the arc current and the arc length (gap size). To be precise the radial magnetic flux density is a critical factor in arc rotation and weld quality. The aim of this study is to explore the interdependence of the magnetic flux density and the existing current in the coils using finite element code ANSYS. The results of this analysis are verified with the available experimental data for steel pipes (outer dia 50mm and 2mm thickness). The results of the numerical simulation emphasize that the magnetic flux density in the gap between the pipes is proportional to the exciting current.

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.

Some studies on the electromagnetic aspects governing the magnetically impelled arcs through experimentation, finite element simulation and statistical analysis

In this study, Magnetically Impelled Arc Butt welding (MIAB) laboratory setup for welding carbon steel tubes of small wall thickness is designed and developed. Magnetically Impelled Arc Butt welding is an efficient two phase process which is used in highly automated factory production lines in high volume industries such as automotive manufactures. In this process, an electric arc generated between aligned and properly gapped pipes are made to rotate along the peripheral butt ends. This arc swiftly rotates along the peripheral edges of the tubes to be welded due to the electromagnetic force resulting from the interaction of the arc current and the externally controlled magnetic field created by magnetic systems. The arc acts as a heating source providing the required heat to the butt ends of the pipes. Further an application of force on the pipe along the axial direction sets the weld. The electromagnetic force responsible for the arc rotation is governed by the magnetic flux density in the gap, the arc current and the arc length (gap size). To be precise the radial magnetic flux density is a critical factor in arc rotation and weld quality. Preliminary trials are conducted to understand the process parameters. Tubes with 45 mm Outer Diameter with 3 mm thickness are used for conducting the investigations. Further, for the first time an attempt is made to analyze the effects of weld input parameters such as welding current, welding voltage, magnetic coil voltage and magnetic coil current on the arc speed in MIAB welding process using software package STATA. The aim of this study also is to explore the distribution of the magnetic flux density in the tube gap region using finite element code ANSYS .The analysis emphasizes that the most significant factor that governs the arc speed is magnetic coil current (that creates magnetic flux density) and the welding current.

Light Band Zone Formation and its Influence on Properties of Magnetically Impelled Arc Butt (MIAB) Welded Carbon Steel Tubes

Magnetically Impelled Arc Butt (MIAB) welding is a solid state welding process especially used in circumferential butt welding of tubes in which heat is generated prior to upsetting by an electric arc moving along the peripheral edges of the weldment with the aid of an external magnetic field. This paper aims at studying the formation of Light Band (LB) zone and its effect on the weld properties of MIAB welding of carbon steel tubes. A detailed microstructural analysis has been carried out to understand the microstructural transformations taking place in Thermo-Mechanically Affected Zone leading to formation of LB zone. Welded samples show better tensile properties with higher upset current as it eliminates LB zone formation at weld interface. For lower upset current, width of the LB zone increases with increase in arc rotation current resulting in lower weld tensile strength.

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.