1985 年 3 巻 3 号 p. 471-477
A possibility of a back bead width control system have been proposed to stabilize the process of one side FCB SAW in which a stationary copper backing plate covered with a flux layer of several milimeter thickness is used as backing.
When a stable welding process is maintained under an adequate welding condition, a signal voltage between the backing copper plate and the plate being welded have beeen detected. The polarity and phase of the detected voltage having a few volt level is well corresponding to those of the arc voltage in case of AC current welding.
In a stable FCB SAW process, the back side bead is mostly formed by a key-hole action of the arc. It is assumed for the reason that the arc penetrates through' the welding groove and the flux layer, then it contacts the copper plate and is reflected to the welding plate. The correlation between the detected voltage level and the back side bead width is recognized.
The similar phenomenon is observed in a key-hole welding by using a transfer type plasma arc welding.
In order to maintain the back bead width constant the detecting voltage is compared with a reference voltage, and then the welding current is controlled by the difference of the above voltages.