S.R. Hansen

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.

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]

Solid State Impact Welds Between Dissimilar Metals Utilizing Vaporizing Foil Actuators: A Microstructural Evaluation

This work aims to study the effect of microstructures of collision welds between various dissimilar metals on the mechanical properties of the weld. In this work, welding between the aluminum-copper, copper-titanium, aluminum-magnesium, titanium-steel, and copper-steel was attempted, and the weld interfaces were examined using optical and electron microscopy. Instrumented peel tests were performed for a qualitative correlation of weld strengths and weld interface microstructure.

Vaporizing Foil Actuator Welding of AA6061 With Cu110: Effect of Heat Treatment Cycles on Mechanical Properties and Microstructure

This work aims to study the effect of microstructure of the weld between aluminum alloy AA6061 and commercially pure copper, Cu 110, on its mechanical properties. AA6061-T6 and T4 aluminum sheets of 1 mm thickness were launched towards copper targets using the Vaporizing Foil Actuator (VFA) tool operating at 8 kJ input energy level. Flyer plate velocities, measured via photonic Doppler velocimetry (PDV), were observed to be approximately 800 m/s. All the welded samples were subjected to instrumented peel testing, microhardness testing, energy-dispersive x-ray spectroscopy (EDS), and SEM. The welded joints had cracks which ran through the continuous intermetallic layers and stopped upon encountering a ductile metallic wave. The welds created with T6 temper flyer sheets were found to have smaller regions with wavy interfaces free of intermetallics as compared to those created with T4 temper flyer sheets. Peel strength tests of the two types of welds resulted in failure along the interface in case of the T6 flyer welds, while the failure generally occurred in the parent aluminum in the case of the T4 flyer welds. Half of the T4 flyer welds were subjected to aging for 18 hours at 160 °C to convert the aluminum sheet back to T6 condition. Although the flyer material did not attain the hardness of the original T6 material, it was found to be significantly stronger than the T4 material. These welds retained their strengths after the aging process and diffusion across the interface was insignificant.Copyright

Vaporizing Foil Actuator: Controlling the Pressure Pulse for Impulse Metalworking

Electrically-driven rapid vaporization of thin conductors produces a high-pressure pulse which can be used to accelerate thin metal sheets to high velocities. Recently, vaporizing foil actuators (VFA) have been applied toward a variety of impulse-based metalworking operations such as collision welding, closed-die forming, embossing, and shearing. To better apply VFA to different purposes, it is necessary to develop an understanding of how variations in the characteristics of the foil actuator affect its mechanical impulse generation. In this work, actuators made out of 0.0508, 0.0762, and 0.127 mm thick full hard temper AA1145 foil were used to launch 0.508 mm thick AA2024-T3 sheets toward a photonic Doppler velocimeter (PDV) probe. Launch velocities ranging between 300 and 1000 m/s were observed over a distance of less than 3 mm, and repeated trials demonstrated repeatable results. Velocity, current and voltage traces were used to examine the effect of deposited energy on average pressure and resulting velocity for foil actuators of various thicknesses. Experiments with annealed foil actuators showed that foil temper had no effect on the evolution of flyer velocity for the given electrical energy input of 8 kJ.Copyright