Secondary-Emission Signals in Plasma Above the Laser Beam Affected Zone during a Vacuum Laser Welding
I.Yu. Letyagin1, V.Ya. Belenkiy2, D.N. Trushnikov3, Sh. Pang4, Ya.V. Lyamin5

1I.Yu. Letyagin, Perm National Research Polytechnic University, Perm, Russian Federation.
2V.Ya. Belenkiy, Perm National Research Polytechnic University, Perm, Russian Federation.
3D.N. Trushnikov, Perm National Research Polytechnic University, Perm, Russian Federation.
4Sh. Pang, Huazhong University of Science and Technology, Wuhan, China.
5Ya.V. Lyamin, Perm National Research Polytechnic University, Perm, Russian Federation.

Manuscript received on 02 June 2019 | Revised Manuscript received on 10 June 2019 | Manuscript published on 30 June 2019 | PP: 3241-3246 | Volume-8 Issue-8, June 2019 | Retrieval Number: H7321068819/19©BEIESP
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Abstract: Development and improvement of laser equipment used for welding allow increasing the share of laser welding in technological processes, especially for obtaining high-quality connections. The current problem of absorbing a portion of the laser beam power by a plasma cloud during laser welding with deep penetration can be solved by using laser welding in a vacuum. Laser welding in a vacuum compared to gas-shielded laser welding makes it possible to obtain a much greater penetration depth at the same power of the laser beam and provides effective protection of the welding zone from the external environment, which is especially important in the welding of active metals. Thus, it is necessary to study the processes in the plasma cloud formed above the zone of action of the laser beam on the metal. Investigation of secondary emission processes in the plasma in the zone of the action of a laser beam on a metal in a vacuum made it possible to numerically simulate the processes in laser welding, depending on the focusing of the laser beam and other technological parameters of laser welding in vacuum. It also allowed recording of the secondary emission current for controlling geometrical parameters of penetration in laser welding. Varying the pressure in the vacuum chamber confirmed the collisional mechanism of damping of secondary-emission current oscillations. The registration of secondary emission signals of ion current is of particular interest, since the detected signal parameters are not associated with the excitation of plasma self-oscillations and, consequently, the magnitude of the ion current directly reflects the density fluctuations of metal vapors flowing out of the channel. The technique can be used in the construction of methods for the operational control of the welding process.
Keyword: Electron current, Ion current, Laser welding in a vacuum, Numerical modeling, Plasma, welding zone.
Scope of the Article: Welding Technology.