A mathematical model of ablation in the keyhole and droplet formation in the plume in deep penetration laser welding
- Univ. of Essex (United Kingdom)
CW CO{sub 2}, CO and Nd:YAG lasers are well established as power sources for the welding of metals. The mechanisms for the coupling of energy from the beam to the weld specimen are important; one such mechanism is Fresnel absorption of laser light in the surface of the metal and another is inverse bremsstrahlung absorption in the plasma of the plume above the surface of the work piece, and in the keyhole produced by the process. For the inverse bremsstrahlung mechanism to work a plasma must be present. It probably forms as a result of ablation of gas from the walls of the keyhole that is then heated up under the action of the laser beam, forming a partially ionized plasma. This emits radiation and so its temperature drops. The radiative losses from argon plasmas have been studied in detail and if metallic plasmas have comparable radiative losses, their temperatures would remain high enough for the Saha equation to predict partially ionized plasmas under conditions of local thermodynamic equilibrium. For partially ionized metallic plasmas in electric arcs data exist that suggest a much higher level of radiation losses. This could lower the temperature of the plasma to a value at which ionization in a state of local thermodynamic equilibrium could be too low to be of significance even for CW CO{sub 2} laser wavelengths. Levels of ionization are lower for CW CO laser wavelengths and probably negligible for the Nd:YAG laser. Plasmas are nevertheless thought to occur when Nd:YAG lasers are used for laser welding. This suggests that some non-equilibrium mechanism is present in laser welding leading to plasma generation. Such a mechanism arises from spray formation at the walls of the keyhole when the temperature is at or slightly above the boiling point of the metal under laser action. Spray ejected from the keyhole walls is quickly vaporized in the beam path. The formation of bubbles in the keyhole wall that gives rise to the spray is studied here.
- OSTI ID:
- 539302
- Report Number(s):
- CONF-961073-; TRN: 97:003387-0028
- Resource Relation:
- Conference: ICALEO `96: 15. international congress on applications of lasers and electro-optics, Detroit, MI (United States), 14-17 Oct 1996; Other Information: PBD: 1996; Related Information: Is Part Of Proceedings of the laser materials processing conference - ICALEO `96. Volume 81; PB: 971 p.
- Country of Publication:
- United States
- Language:
- English
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