Collision Behavior in Magnetic Pressure Parallel Seam Welding of Aluminum Sheets

Abstract

Magnetic pressure seam welding has attracted attention as a new joining method for aluminum thin plates. Magnetic pressure seam welding is a collision welding process, utilizing electromagnetic force as the acceleration mechanism. The electromagnetic seam welding is a method of abruptly adding a high density magnetic flux around a metal material and utilizing the generated electromagnetic force to deform the thin plate at high speed and pressure welding. This paper deal with the deformation behavior of parallel aluminum seam welded aluminum sheet. Numerical analysis of the dynamic deformation process of the metal plate is performed by the finite element method. The sample used for this analysis is assumed to be a thin plate made of aluminum (A1050-H24, width100mm, thickness 1mm) and composed of quadrilateral elements of plane strain. The experimental results show that the collision speed between the aluminum plates is sufficiently reproduced. The impact point velocity between the aluminum plate surfaces was very high at the initial collision point but decreased continuously during welding. It was also found that the smaller the gap is, the faster the collision point moving speed becomes. Introduction Aluminum has higher electrical conductivity and thermal conductivity than iron, so welding is difficult due to low heating efficiency. In previous studies, there is a report on the magnetic pressure seam welding method [1]-[14]. Magnetic pressure seam welding is a collision welding process similar to explosive welding and utilizes electromagnetic force as an acceleration mechanism. Magnetic pressure seam welding accelerates and collides a certain metal plate (flyer plate) to another stationary metal plate (parent plate) by using electromagnetic force. When an impulse current from a capacitor bank passes through a flat one-turn coil, a magnetic flux is instantaneously generated in the coil. The eddy currents are induced in insulated flyer plate in the coil. In magnetic pressure parallel seam welding, one-turn coils are arranged in parallel. A part of flyer plate along the longitudinal direction of the coil bulged toward a parent plate, then flyer plate collided and was welded to a parent plate. At the time of the high-speed collision, metal jets are emitted in the welding interface of the specimen [7]. The collision point velocity and collision angle are determined by the primary and induced electromagnetic force. True metallic bonding is achieved at the mating interface if contact takes place above an appropriate collision point velocity and collision angle [15]. The purpose of this paper is to discuss, the dynamic deformation behavior of magnetic pressure parallel seam welding of aluminum sheets. Welding principle The welding principle is shown in Fig. 1. Magnetic pressure parallel seam welding uses electromagnetic force to accelerate one metal sheet (flyer plate) against another stationary metal Explosion Shock Waves and High Strain Rate Phenomena Materials Research Forum LLC Materials Research Proceedings 13 (2019) 47-52 https://doi.org/10.21741/9781644900338-8 48 sheet (parent plate). When a high magnetic field B suddenly occurs and enters the metal sheet, eddy current (current density i) passes through the metal sheet. As a result, the electromagnetic force of Eq. 2 acts mainly on the flyer plate and it is accelerated away from the coil and collides rapidly with the parent plate [10]. The eddy current i, electromagnetic force f and Joule heat Q are given as follows. κ and B are electric conductivity and magnetic flux density at aluminum sheet. When the residual inductance of the electromagnetic forming apparatus is large, it becomes difficult for a large current to flow through the one-turn coil, so the magnetic pressure also becomes small and it is difficult to join. Since the inductance of the coil of the multi-turn coil is higher than that of the one-turn coil, the current flowing through the coil can be increased and the magnetic pressure can be increased. rot i = −κ ∂B ∂∂ (1)