Anupam Vivek

Microstructures and Mechanical Properties of Laser Penetration Welding Joint With/Without Ni-Foil in an Overlap Steel-on-Aluminum Configuration

The microstructures and mechanical properties of laser penetration welding joints with/without Ni-foil in an overlap steel-on-aluminum configuration were investigated. The interfacial structure between fusion zone and aluminum alloy without Ni-foil consists of FeAl/FeAl3. After the Ni-foil is added, the interfacial structure transforms into Ni1.1Al0.9/FeAl3, and the molten pool of aluminum alloy is expanded, which leads to the formation of the NiAl3 between Ni-foil and the molten pool. A banded structure composed of β(Fe, Ni)Al appears whether the joints are made with/without Ni-foil over the reaction zone. It was found that the Ni-foil enhanced tensile property of the joint, expanded usable processing parameters, and decreased microhardness of the intermetallic compounds. The enhancement of mechanical properties is attributed to the improvement of the toughness of the joint made by Ni-foil.

Laser impact welding application in joining aluminum to titanium

Thin metal foil joining has wide applications in medical device and microelectronics. In this paper, laser impact welding was implemented to join aluminum foil to titanium sheet. The velocity of Al flyer was measured with photonic Doppler velocimetry. The maximum velocity reached up to 1000 m/s within 0.2 μs. Varied thickness (25–250 μm) Al flyer was successfully welded with Ti target. Weld strength was measured with peel test. Weld area was estimated with resistance measurement method. The effect of laser spot size, flyer thickness, standoff distance on weld strength, weld area, and microstructure was analyzed. The microstructure was studied with scanning electron microscopy (SEM). By comparing the amplitude and wavelength of the waves at the bonding interface, it is suggested that the wave formation was related to the impact velocity. SEM back scattered electron image did not show apparent diffusion across the weld interface. Both twinning and severe plastic deformation were observed at Ti side along th...

High strain rate metalworking with vaporizing foil actuator: Control of flyer velocity by varying input energy and foil thickness

Electrically driven rapid vaporization of thin metallic foils can generate a high pressure which can be used to launch flyers at high velocities. Recently, vaporizing foil actuators have been applied toward a variety of impulse-based metal working operations. In order to exercise control over this useful tool, it is imperative that an understanding of the effect of characteristics of the foil actuator on its ability for mechanical impulse generation is developed. Here, foil actuators made out of 0.0508 mm, 0.0762 mm, and 0.127 mm thick AA1145 were used for launching AA2024-T3 sheets of thickness 0.508 mm toward a photonic Doppler velocimeter probe. Launch velocities ranging between 300 m/s and 1100 m/s were observed. In situ measurement of velocity, current, and voltage assisted in understanding the effect of burst current density and deposited electrical energy on average pressure and velocity with foil actuators of various thicknesses. For the pulse generator, geometry, and flyer used here, the 0.0762 mm thick foil was found to be optimal for launching flyers to high velocities over short distances. Experimenting with annealed foil actuators resulted in no change in the temporal evolution of flyer velocity as compared to foil actuators of full hard temper. A physics-based analytical model was developed and found to have reasonable agreement with experiment.

Depiction of interfacial morphology in impact welded Ti/Cu bimetallic systems using smoothed particle hydrodynamics

Numerical simulations of high-velocity impact welding are extremely challenging due to the coupled physics and highly dynamic nature of the process. Thus, conventional mesh-based numerical methodologies are not able to accurately model the process owing to the excessive mesh distortion close to the interface of two welded materials. A simulation platform was developed using smoothed particle hydrodynamics, implemented in a parallel architecture on a supercomputer. Then, the numerical simulations were compared to experimental tests conducted by vaporizing foil actuator welding. The close correspondence of the experiment and modeling in terms of interface characteristics allows the prediction of local temperature and strain distributions, which are not easily measured.

Impact Welding of Aluminum Alloys 6061 and 5052 by Vaporizing Foil Actuators: Heat-Affected Zone Size and Peel Strength

Joining aluminum alloy sheets is increasingly important in manufacturing. Traditional welding techniques create a heat-affected zone (HAZ) around the joint; however, solidstate joining methods such as impact welding produce joints without significant heat. Here, electrically vaporized foil actuators (VFA) provided the high-pressure pulses needed for impact welding. 0.96 mm thick AA6061-T6 and 0.76 mm thick AA5052 were joined in lap and spotlike configurations, at a variety of impact velocities. The welds failed in coach-peel outside the joint interface. The 5052 hardened within 100 lm of the interface. The 6061-T6 may have softened slightly within 50 lm of the interface. [DOI: 10.1115/1.4030934]

Numerical Modeling of High-Velocity Impact Welding

To support the lightweighting aim in the automotive industry, High-Velocity Impact Welding (HVIW) can be used to join dissimilar metals. The manufacturing industry often relies on numerical simulations to reduce the number of trial-and-error iterations required during the process development to reduce costs. However, this can be difficult in high strain rate manufacturing processes where extremely high plastic strain regions develop. Thus, a traditional Lagrangian analysis is not able to accurately model the process due to excessive element distortion. In order to further understand the science behind HVIW processes and benefits of various numerical simulation methodologies, two methods were utilized to simulate Al/Fe bimetallic system which is of interest for the automotive industry. First, a Smoothed Particle Hydrodynamics (SPH) model of two impacting plates was created. Using SPH method, metal jet emission was investigated which previously was impossible. The results then were compared with an Arbitrary Lagrangian-Eulerian (ALE) method. Finally, the numerical results were compared with experimental tests using a Vaporizing Foil Actuator Welding process.

Electromagnetically Assisted Sheet Metal Stamping and Deep Drawing

Factors such as limited draw in and friction against tool surfaces cause difficulty in forming of sheet metals. Most of the strain tends to localize in the wall of the formed part while the bottom, in contact with the punch surface, and the flange, held down with the blank holder do not undergo much deformation. Augmentation of conventional forming processes with electromagnetic forming has been proposed as a method to attain higher draw depths by distributing strains more uniformly and encouraging draw in. In separate experiments, electromagnetic forming coils were embedded either in the bottom of the punch or in the blank holder. In both cases, multiple electromagnetic pulses in the coils followed by movement of the punch lead to higher draw depth as compared to corresponding stamping or deep drawing processes.

Benchmarking and Refining the Vaporizing Foil Actuator Spot Welding Process

Impact spot welding implemented by the vaporizing foil actuator welding method has been studied. With significantly lower input energy levels as compared to resistance spot welding, similar and dissimilar lap welding of aluminium alloys (AA) of types 5052 and 7075 was implemented. The dissimilar welds between 2 mm thick AA5052 and 2.3 mm thick AA7075 were created with 4 kilojoules input energy, whereas the similar welds between 1 mm thick AA5052 sheets required only 0.6 kilojoules. Flyer sheet velocities of approximately 750 m/s were measured with a PDV system. Microhardness measurements, performed across the dissimilar weld interfaces, showed no softening of the base materials due to the welding process. A few distinct welding configurations were investigated for improving process feasibility and obtaining the highest possible weld strength. Lap shear tests and pry tests revealed that the configuration of the starting weld geometry greatly affected weld quality.

Vaporizing Foil Actuator: a Tool for Creating High‐Pressure Impulses for Metalworking

Impulse based metalworking has significant advantages, in that short time scales change the fundamental nature of the forming process and short duration impulses can be used with much lighter and more agile equipment because large static forces do not need to be resisted. Electrically vaporized thin conductors, termed as Vaporizing Foil Actuators (VFA), can be used to develop significantly high driving pressures over short time scales. The driving pressures can be a few GPa’s, and have been used to launch sheet metal workpieces to velocities in excess of 1 km/s. Applications include, but are not limited to, impact welding, forming, embossing, shearing, tube joining, and powder compaction.

Use of Vaporizing Foil Actuator for Impact Welding of Aluminum Alloy Sheets with Steel and Magnesium Alloys

The vaporizing foil actuator (VFA) is a novel tool for impulse-based metal working operations. In this work, it has been used for impact welding of aluminum flyer sheets to high-strength steel and magnesium plates. Aluminum alloy 6061 sheets of 0.81 mm thickness were launched to velocities in excess of 800m/s and found to weld to both the target materials investigated: HSLA A588 steel and AM60B magnesium alloy. Grooved as well as flat target plates were utilized. Welding with grooved target plates was found to be not very robust as the weld samples came apart during sectioning. However, the flat targets welded successfully, and during mechanical testing, failure was found to occur outside the joint. The weld interface morphology for each material system and configuration has been shown. Some improvements to the grooved-target experimental configuration are also demonstrated.