Impact Seam Welding with Magnetic Pressure for Aluminum Sheets

This paper describes a new seam welding technique for aluminum sheets and its experimental results. When an impulse current from an energy-stored capacitor bank passes through a flat one-turn coil, a high-density magnetic flux is suddenly generated in the coil. Eddy currents are induced inside the overlapped ends of two aluminum sheets (thickness 1.0 mm each) with a gap placed in the coil. The two sheets are suddenly pressed together by magnetic pressure applied onto them. If the moving velocity of the sheets is high, the both surfaces are cleared by an effect of the collision which is known as explosive welding, and then can be joined both by the magnetic pressure onto them and by the joule heat generated in them. A bank energy required for this impact seam welding of an area 5×50 mm 2 is less than 1 kJ. I ntroduction Spot welding method is conventionally used for welding of aluminum sheets. In this method, a large current passes almost instantaneously between electrodes pressed on each side of the overlapped ends of two aluminum sheets being welded to make a spot joint by resistance heating (Joule effect). Although the seam welding of aluminum sheets is possible by continuous spot welding with roller electrodes, only a few examples on the application have been reported. The reason is that the heating effect on aluminum is low due to its higher electrical and thermal conductivities compared with those of steel and the lifetime of electrode used in cyclical elding of aluminum sheets is short due to severer alloy-yielding fusion. w In the previous papers we proposed a method of seam welding for aluminum sheets in contact, reporting its experimental results [1]. In our method with a flat one-turn coil instead of electrodes, sheet-materials with higher electrical conductivity such as aluminum undergo a better effect of pressure welding, and can be joined instantaneously both by magnetic pressure and Joule heat without high mechanical pressure. The seam welding for Al-sheets with a gap proposed in this paper has a better effect than our former method. We deal with effects of a gap between aluminum sheets 50 mm wide. P rinciple of Welding The principle of the impact welding method proposed by us is shown in Fig. 1: cross section view of two aluminum sheets with a gap (before welding) to which a magnetic field (magnetic flux density B) is applied. When a high-density flux is suddenly generated on both sides of the overlapped parts of two aluminum sheets with a gap and penetrates into them, eddy currents (current density i) pass through them to hinder its further penetration. As a result, an electromagnetic force of i ×B acts on the two parts and presses them together simultaneously so that they collide with each other. At the moment of collision the colliding surfaces can be cleared by a large kinetic energy getting before the collision. The higher the moving velocity of the parts is, the larger effect of the collision velocity just before a collision is. Even after the collision, the cleared surfaces are being pressed together by electromagnetic force. The eddy currents i are given by Eq.1 and the magnetic pressure p is equivalent to the electromagnetic Materials Science Forum Online: 2004-09-15 ISSN: 1662-9752, Vols. 465-466, pp 231-236 doi:10.4028/www.scientific.net/MSF.465-466.231 © 2004 Trans Tech Publications Ltd, Switzerland All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications Ltd, www.scientific.net. (Semanticscholar.org-11/03/20,14:30:27)