Abstract: A tool comprising tongs with two pivoted arms and a release system. The two arms each bear, at their respective ends, pressure members. A drive motor causes the arms to pivot with respect to one another, either to close them and thus permit the pressure members to grip the part to be treated, or to open them and permit the release of the part with respect to the tongs after treatment. This tool in addition includes a release system which insures that the two pressure members are well separated from the part after actuation of the opening of the arms. The release system includes a coupling device adapted to actively control the opening and closing of the arms using a fraction of the power of the drive motor. Preferably, this coupling device is an electrically controlled clutch.

Abstract: For improving the quality of welding operations, in a process for alternating current welding, in which during a period the actual r.m.s., welding current is measured and the phase displacement of the use of current flow during the next period of the a.c. current is regulated. Variations of the actual r.m.s. welding current during all the welding periods already performed are taken into account and compared with a desired r.m.s. current during the welding period to be performed. A welding apparatus for alternating current welding using two welding electrodes, a power supply for the same and a device for regulating the r.m.s. welding current during each a.c. voltage period has a computer for taking into account variations of the actual r.m.s. welding current during preceding welding periods of a welding operation compared with a desired r.m.s. welding current flow during the further welding periods to be performed of the particular welding operation.