Papers by Author: Tomokatsu Aizawa

Abstract: 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.

Abstract: A new welding method, magnetic pressure seam welding, was used to lap join dissimilar metals (Al-Fe, Al-Ni and Al-Cu). The circuit for magnetic pressure seam welding consists of a capacitor, an electric discharge gap switch, and a plate-type coil. The overlapped metal plates are placed over the coil. When an impulse current from an energy-storage capacitor bank passes through the coil, a high-density magnetic flux is suddenly generated around the coil. The generated high-density magnetic flux lines cross the end of the overlapped plates. Eddy currents are induced mainly inside the Al plate because it has a high electrical conductivity. Both the Joule heat generated in the plates and the magnetic pressure applied from the Al side promote the joining of the lapped plates. The welding is normally achieved within 10 μs. This results in very little microstructural change in the parent plates aside from the area around the weld interface. Strong lap joints were obtained for every metal combination and no tensile fracture took place in the weld region. A characteristic wavy morphology was observed at the weld interface. An intermediate phase layer was also observed at the weld interface. TEM observation revealed that the intermediate layer consisted of fine Al grains and intermetallic compound particles dispersed among the Al grains. The growth direction of the wave, the welding condition dependency of the wavelength and the amplitude of the interfacial wave were intensively investigated in order to clarify the welding mechanism of this method.