Study on the Flash Welding Phenomena of Steels (4th Report)

Investigation on the Flash Welding without Upset Current

Abstract

Further study is made using three types of circuit shown in Fig. 1, because the arc plays an important role in flashing action.
Oscillograms of flashing current in late stage of flashing process using three circuits are shown in Fig. 3. In the case of circuit I, the arcing current is held to continue for comparatively long duration by large leakage inductance of welding transformer (L₀) In the case of circuit III, however, the arcing current decreases rapidly, because the arc energy is only supplied from the stored energy in the small inductance L. This means small heating per one arc.
The short circuit current increases rapidly for circuit III for the same reason mentioned above. The rapid increase of short circuit current is effective to break the newly formed short circuit path due to the local concentration of joule's heat. The above mentioned characteristics concerning circuit III result' in frequent splashing of many droplets of small sizes under the same platen velocity as that in circuit I.
Circuit characters affect the formation of molten metal layer in flashing period. In the case of circuit I, the molten metal layer is observed to locate on a part of test piece end. It is supposed that the molten metal on the central part is splashed off by powerful arc force. But, in the circuit II or III, molten metal layer of 0.5-0.2mm thickness is observed all over the end of test pieces.
Thus, if the molten metal layer is formed all over the end of test pieces by selecting the circuit constant, welds with good mechanical properties are obtained, even though upset current is not allowed to flow by cutting off artificially the power circuit as soon as upsetting begins.