Sachin D. Kore

Electromagnetic impact welding of Mg to Al sheets

Abstract Magnesium (Mg) and aluminium (Al) alloys have been lap welded using an electromagnetic impact welding technique. Metallographic examination of the welds has revealed sound and defect free interfaces. Complete metal continuity has been observed with a characteristic wavy interface. X-ray diffraction analysis has shown no intermetallic phases and suggested that this electromagnetic technique is a solid state welding process. All the shear strength samples welded with discharge energy of 6·7 kJ failed away from weld either in the plastically deformed zone or in the base metal. Optimum discharge energy has been determined as 6·7 kJ based on the shear strength results of the welds.

Numerical modeling of electromagnetic welding

Feasibility of electromagnetic welding of flat sheets is ascertained by comparing the minimum impact velocities determined by using software ANSYS/EMAG and ABAQUS with the required minimum velocity obtained from analytical considerations. Magnetic forces acting on the sheets are computed from ANSYS/EMAG simulations. The velocity of impact and the pressure profile acting on the sheets are found from ABAQUS simulations. A criterion for weld formation is subsequently arrived at based on the simulations, which is further validated using experimental results. The reasons for no-weld zone in Al-to-Al EM weld and complete metal continuity (absence of no-weld zone) in Al-to-SS EM weld have been analyzed based on the numerical and experimental results.

Electromagnetic Impact Welding of Al-to-Al–Li Sheets

The potential for weight savings resulting from the low density and high stiffness of aluminum-lithium (Al―Li) alloys and the difficulty in fusion welding of these alloys led to this study of solid state welding of Al―Li alloys for its potential application in the aerospace and automobile industries. The present study demonstrates the feasibility of electromagnetic (EM) welding of Al-to-Al―Li sheets by using Al drivers to drive the electrically poor conductive Al―Li sheets. A study has been carried out to characterize the electromagnetic impact welding of Al-to-Al―Li sheets of 1 mm thickness. Specific heat treatment cycle need to be followed prior to EM welding of Al―Li sheets. The results of the microstructure and tensile shear strength tests are reported.

Study of Wavy Interface in Electromagnetic Welds

Wavy interface is a characteristic of an impact weld. Electromagnetic pulse welding is a solid state welding process, which produces a weld between two mating surfaces at high velocity of impact. In this paper studies on metallurgical characterization of electromagnetic welds to find the presence or absence of wavy weld interface, by using optical microscope and scanning electron microscope, are reported. EM welds of Al to Al do not show wavy interface due the low energy of impact. EM welds of Al to Steel show wavy weld interface due to instability at the weld interface. Studies have revealed that discharge energy and critical velocity of impact are the important parameters for creating stronger electromagnetic welds and the wavy weld interface.

Fully Coupled Numerical Simulation of Electromagnetic Forming

Electromagnetic forming (EMF) is a typical high speed forming process using the energy density of a pulsed magnetic field to form work pieces made of metals with high electrical conductivity like aluminum. In view of new lightweight constructions, special forming processes like EMF gain importance for the associated materials. In this paper modeling of electromagnetic sheet metal forming process is carried out by using commercial finite element software LS-DYNA®. A fully coupled numerical simulation method has been incorporated to study the interaction of the electromagnetic field and the structural deformation via transient analysis. Studies on the effect of first current pulse in electromagnetic forming are reported in the paper.

A three-dimensional fully coupled thermo-mechanical model for Self-reacting Friction Stir Welding of Aluminium AA6061 sheets

In the present work a three dimensional model of self-reacting friction stir welding in aluminium alloy AA6061 has been developed based on the Computational Fluid Dynamics (CFD) approach using COMSOL Multiphysics software. The temperature dependent material properties have been incorporated in the model from available literature. A slip-stick contact between the workpiece and tool surface has been considered with the slip factor varying linearly with distance. The methodology adopted has been validated with experimental results available in the literature. The temperature distribution observed has been found to be asymmetric about the weld centre line. The maximum temperature has been observed on the advancing side of the weld. However, the temperature distribution across the thickness has been found to be almost symmetric about the mid thickness plane. An hourglass shaped temperature distribution has been observed across the cross-section of the weld. The material flow velocity distribution shows that the deformation zone is limited to a very small region around the tool.

Electromagnetic forming analysis of AA5182 at elevated temperatures

Electromagnetic forming is a high-velocity, unconventional forming process, in which a high magnetic field is used to form a metal workpiece. Light weight metals such as aluminium and magnesium and their alloys are generally formed through this type of forming process. Increasing the temperature would lead to a decrease in the flow stress of a material. Thus, a metal can be deformed easily at elevated operating temperatures for the case of conventional forming. In this paper, high-velocity electromagnetic forming analysis of aluminium alloy AA5182 has been carried out in a commercially available FEM package, LS Dyna®. The deformation behaviour, in the case of electromagnetic forming, has been studied for various elevated temperatures in order to determine the feasibility of the process at high temperatures.

Studies on Temperature Distribution in Electromagnetic Welding Process

Electromagnetic welding (EMW) is a solid state impact welding technique which uses pulsed electromagnetic field for welding electrically conductive work pieces like aluminum. High velocity of impact created by the electromagnetic force causes the removal of oxide layer from the weld interface. A fully coupled numerical analysis, incorporating the equivalent electric circuit of EMW, electromagnetic field propagation, heat transfer, and dynamic elasto-plastic deformation, has been carried out using LS-DYNA EM module. The numerical simulation results for the EM weld feasibility, deformation pattern, temperature distribution and velocity of impact are reported here and corroborated with the previously published literature. It is observed that the temperature rise is not significant to cause the melting of Al sheets indicating there will not be any intermetallics. Hence, present paper is important for welding dissimilar metals for automobile components. Metallographic studies have also revealed absence of any coarse or columnar grain structures at the weld interface.

Electromagnetic Pulse Crimping of Al-Tube on DP Steel Rod

The electromagnetic pulse crimping is a high energy, high strain rate, high velocity, and green materials joining or surface coating technique. Joining of dissimilar materials is difficult due to their physiochemical properties that are seldom compatible or similar. Therefore, electromagnetic pulse crimping which is solid-state joining technique can be an alternative for joining dissimilar materials. In the present work, composite rods were produced by the electromagnetic pulse crimping technique, which was characterized by a uniform crimping of the flyer tube on the base rod perimeter. The materials used were Al 1050 as flyer tube and dual-phase (DP) steel as a base rod. Numerical simulations were carried out for finding out the optimized parameters for crimping and then experiments were conducted on the optimized parameters. The results obtained from the simulations revealed that for the successful crimping, a minimum value of collision velocity, plastic strain, electromagnetic pressure, and standoff distance must be maintained. The post-process current obtained from the simulations and first peak of the discharge current measured in the experiments was compared. The variation in the maximum value of discharge currents in simulations from the experimental values was found to be 2, 3, and 7% at 2.5, 2.6, and 2.9 kJ of discharge energy. The outer diameter of the successfully crimped samples was measured and compared with the outer diameter obtained from the simulations and found a maximum of 6.6% variation in the simulation value from the experimental value. The optical microscope image was analyzed and it was found that the Al-tube was crimped on the DP steel rod with a negligible gap. Further, pullout tests and hardness tests at the interface were performed to test the strength and hardness of the joints, respectively.

Finite Element Method and Experimental Study of Self-reacting Friction Stir Welding of Aluminium Alloy AA6061-T6

Self-Reacting Friction Stir Welding is a variant of Friction Stir Welding (FSW) in which through a modification in the tool design, welding can be carried out in the absence of a backing plate. In this variant, the tool has two shoulders connected by the pin. Due to this small modification in tool design, the process is significantly influenced. In the present work, the effect of tool traverse speed using a fixed gap bobbin tool on the weld quality has been studied using a Finite Element Method (FEM) model and experimental study. The present work has been carried out on 4-mm-thick aluminium alloy AA6061-T6 plates, which have been welded in butt configuration. Uniaxial tensile tests of the welded samples have been carried out to correlate the traverse speed with yield strength and ultimate tensile strength. Three-point bend tests have been carried out to expose any flaws present in the joints and compare mechanical properties on the two sides of the joints. In addition to this, the joint macrostructure has been studied and has been compared with the stir zone developed in the FEM model. The microstructure in the various zones of the welded joints for different traverse speeds has been studied and compared with the grain structure of the base material to reveal its effect. A relationship has been established between the process parameters and the resulting average grain size in the joint.