Keigo Okagawa

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

Electromagnetic Bulging of Stainless Steel Sheet by Using Flat One-Turn Coil

In this paper, we describe an electromagnetic bulging for a SUS304-O stainless steel sheet (0.15 mm thick) and its experimental results. In the die forming, the flat one-turn coil is adopted for the bulging of the SUS304-O sheet, when an aluminum sheet (0.3 mm thick) as a driving plate (driver) is used together. When an impulse current from an energy-storing capacitor bank passes through the flat one-turn coil, a high-density magnetic flux is suddenly generated around the coil. Eddy currents are induced in the driver placed on the coil. The SUS304-O sheet is pressed by an electromagnetic force generated in the driver, leading to bulge into a meandering groove with small concave shape. The bank energy required for the bulging of 12mm wide, 60mm long and 0.43mm high is about 4.5 kJ, and the obtained workpiece does not almost have wrinkles and curves.

Influence of Collision Velocity and Collision Time on Joining Property in Welded Sheets Obtained by Magnetic Pulse Welding

In this paper, a number of factors influencing the joining property of sheets welded by a magnetic pulse welding are described. An electromagnetic force deforms a moving sheet, and the height of the sheet is governed by both the force and the properties of the sheet. Some information obtained from the first collision time is very useful, so two sheets with a gap can be joined with each other after the first collision. The relationship between the collision time and the gap length for an aluminum sheet is examined by 2.0kJ discharge energy experiments, and an approximation curve of this relationship is drawn. The velocity of the moving sheet is found by differentiation of the curve. The relationship between shearing load with the welded sheet and the gap length is also examined. Similar results have also been obtained for a copper sheet, and the relationship between the shearing load and the collision velocity has been shown for two materials. It has been clarified that the shearing load is distributed into three areas depending on the collision velocity. Therefore, the collision velocity is the main factor influencing the joining property of welded sheets. It has also been clarified that another influencing factor is the first collision time.

One-metre-long seam welding of aluminium sheets by applying magnetic pressure: introduction of new connection method of long sheet metal ends

Thin aluminium sheet, which is characteristically light and has high strength per unit weight and good workability, is widely used in, for example, industrial products, household products, and soft drink cans. In a production line capable of continuous surface treatment and heat treatment of thin aluminium sheet, it is necessary to join the rear end of the preceding aluminium sheet to the leading end of the next aluminium sheet coming onto the line. There are various methods of performing this joining technique, which is known as ‘sheet connection’. In many cases, the ends of the sheets are brought to a temporary halt to be joined. Electromagnetic seam welding – 8 is used for sheet connection and this has the extremely short welding time of 10ms. Here, we report on basic experiments in electromagnetic seam welding of long aluminium thin sheets of 1 m or longer, on various sheet connection methods, the fabrication of connections for experimental line treatment and, finally, on a new sheet connection method.