Flash butt welding process has been widely used in the fabrication of wheel-rims in the automobile industry because of its high production efficiency. On the other hand, a DC butt welding process has been recently developed and put into practice for wheel-rim production instead of the flash butt welding process. The reasons seem to be higher production efficiency, energy savings and clean environment (no flash). There are many reports1)∼3) on flash butt welding, but there are little, if any reports on DC butt welding.
In this report, the DC butt welding process was studied from the view point of comparison with the flash butt welding process. The weld defect formed in flash butt welding is mainly oxide inclusion (Si-Mn-Al oxide) at weld interface. On the other hand, in DC butt welding the cold weld and overheat cracking due to heat input are main weeld defects. Such defects in DC butt welding are controlled by the welding conditions; that is, welding current, welding time and electrode pressure which are 3 main control factors in resistance welding, such as spot welding, as heat input of DC butt welding is generated by joule's heat. In addition, though the heat input along the weld line is uniform in flash butt welding, it is non-uniform in DC butt welding. It is generally generated near both plate side edges. In the case of higher heat input, the growth of the overheat cracking is initiated at both plate side edges. This phenomena that nonuniform heat input is generated is characteristic of DC butt welding.
Maximum hardness of welded joint is higher in DC butt welding than that in flash but welding, because the cooling rate is higher in DC butt welding due to lower heat input.