9.5 Summary
273
under atmospheric pressure, there is no obvious vortex under vacuum, which
is good for the reduction of porosity defect.
(5) The penetration depth increases obviously under vacuum compared with that
under atmospheric pressure. The mechanisms proposed recently for penetration
depth increase are systematically introduced and clarified: the boiling temperature of materials under vacuum decreases obviously, which allows more laser
energy to be used in the penetration direction; this is the main reason for
the increase of the penetration depth; the inverse bremsstrahlung absorption
effect mainly takes an effect on the long wavelength laser welding (e.g. CO 2
laser welding); the scattering and fraction of metal vapor plume is an important factor in penetration depth increase in the short wavelength laser welding
under vacuum, especially in the high-power laser welding; but this important
factor only accounts for only 10–20% of penetration depth increase and is thus
not the main reason for the increase.
(6) The penetration depth will not continue to increase as the ambient pressure
decreases to a certain value. The physical phenomena and mechanism of the
finite increase of penetration depth under reduced ambient pressure are introduced and clarified. The critical ambient pressure theory and formula for the
vacuum laser welding process are also introduced. These findings provide
guidance for the design of industrial vacuum chambers, and promote the
development and industrial application of vacuum laser welding technology.
273
under atmospheric pressure, there is no obvious vortex under vacuum, which
is good for the reduction of porosity defect.
(5) The penetration depth increases obviously under vacuum compared with that
under atmospheric pressure. The mechanisms proposed recently for penetration
depth increase are systematically introduced and clarified: the boiling temperature of materials under vacuum decreases obviously, which allows more laser
energy to be used in the penetration direction; this is the main reason for
the increase of the penetration depth; the inverse bremsstrahlung absorption
effect mainly takes an effect on the long wavelength laser welding (e.g. CO 2
laser welding); the scattering and fraction of metal vapor plume is an important factor in penetration depth increase in the short wavelength laser welding
under vacuum, especially in the high-power laser welding; but this important
factor only accounts for only 10–20% of penetration depth increase and is thus
not the main reason for the increase.
(6) The penetration depth will not continue to increase as the ambient pressure
decreases to a certain value. The physical phenomena and mechanism of the
finite increase of penetration depth under reduced ambient pressure are introduced and clarified. The critical ambient pressure theory and formula for the
vacuum laser welding process are also introduced. These findings provide
guidance for the design of industrial vacuum chambers, and promote the
development and industrial application of vacuum laser welding technology.