Investigation of Processes in the Keyhole of Electron-Beam Welding by Monitoring the Secondary Current Signal in the Plasma

Use of a Secondary Current Sensor in Plasma during Electron-Beam Welding with Focus Scanning for Process Control

“…Studying the secondary current using an electron collector, which is positioned above the welding puddle and used to sample the current from the plasma, has shown that in addition to the beam current the size of this current is determined by the shape and dimensions of the penetration channel, conditions of the flow of current in the plasma, the position of the beam's area of interaction with the metal, the position of the beam's focus in the penetration channel, and so forth [28,29]. Therefore, the secondary waveform from a non-self-sustained discharge of current in plasma may be expressed as follows [30]:…”

“…The recommended distance from the collector to the welding zone is 20-50 mm, which lowers the level of ion-acoustic instability in plasma Figure 11: Functional diagram of the modified focus control system: 1, electron gun; 2, focus coil; 3, amplifier for the focus coil current; 4, electron collector; 5, modulation block; 6, bias voltage source; 7, load resistor; 8, high-frequency filter; 9, synchronous detection block for harmonic 1 ; 10, control block; 11, synchronous detection block for harmonic 1 ; 12, division block. [28,34], which arises when exciting a non-self-sustained discharge. The synchronous detection block, whose operation is explained by the block diagram in Figure 10, processes the secondary waveform in accordance with (24).…”