Controlled bridge transfer (CBT) gas metal arc process for steel sheets joining

Abstract

In non-pulsed gas metal arc welding (GMAW), spatter can be reduced by lowering the short circuit current to a low level just before the rearcing period. The reduction of spatter requires an improvement in the accuracy of predicting the rearcing by stabilising the metal transfer and improving the robustness of the accuracy against disturbances. The controlled bridge transfer (CBT) process optimises the accuracy of predicting the rearcing in real time in response to the metal transfer, in order to realise spatter reduction and stable arcs in non-pulsed GMAW. Traditionally, GMAW is carried out using electrode positive polarity. However, this polarity is not sufficient for welding extrathin steel sheets, specifically those thinner than 1·0 mm. With an electrode negative (EN) CBT process, although some slight arc voltage fluctuation occurs caused by the behaviour of the cathode spots on the tip of the wire during in EN polarity GMAW, instantaneous voltage is used, through a command computation, to improve the transient response against the disturbance. Consequently, a stable arc can be obtained without increasing the number of short circuits in a unit time to obtain spatter free welds.