Spectroscopic characterization of laser-induced plasma created during welding with a pulsed Nd:YAG laser

Abstract

A spectroscopic study of a laser-induced plume created during the welding of stainless steel and other materials (iron and chromium) has been carried out. A pulsed Nd:YAG laser of 1000 W average power is used. The evolutions of the electron temperature and electron density have been studied for several welding parameters. We use working powers from 300 to 900 W and pulse durations between 1.5 and 5 ms. The influence of shielding gases like nitrogen and argon has been taken into account. Temperature and density calculations are based on the observation of the relative intensities and shapes of the emission peaks. We assume that the plasma is in local thermal equilibrium. The temperature is calculated with the Boltzmann plot method and the density with the Stark broadening of an iron line. The electron temperatures vary in the range of 4500–7100 K, electron density between 3×1022 and 6.5×1022 m−3. The absorption of the laser beam in the plasma is calculated using the Inverse Bremsstrahlung theory.

Effects of Different Shielding Gases and Power Waveforms on Penetration Characteristics and Porosity Formation in Laser Welding of Inconel 690 Alloy

“…Three different shielding gases, namely Ar, He and N 2 , were used to provide face shielding. The shielding gas nozzle had a diameter of 4 mm and was arranged at an angle of 25 to the workpiece. The shielding gas was delivered with flow rates of 10 L min À1 , 16 L min…”

“…[22][23][24] However, in Nd:YAG laser welding, laser absorption in the plume is very weak, 25) and therefore the plume volume has a lesser influence on the penetration depth. Consequently, the penetration depths identified in the present study are very similar despite the fact that the plumes formed under the three shielding gases are quite different in size (as shown Fig.…”

Characteristics of plasma plume in fiber laser welding of aluminum alloy

“…The T e reflects the heat input, while the N e is closely associated with the evaporation and the ionization of the materials. The T e can be deduced by relative intensities of two spectral lines of the same element under same ionization stage if the plasma is in local thermal equilibrium (LTE) [19][20][21][22]. The assumption of LTE is fulfilled when the N e is high enough so that 18 …”

Advances of OCT Technology for Laser Beam Processing

“…Moreover, the optical properties of the laser-induced plasma during welding may distort the three dimensional data set due to refractive index change and consequently may lead to reduced keyhole depth. However, spectroscopic characterization of laser-induced plasma created during welding of stainless steel with a pulsed Nd:YAG laser by Lacroix et al [9] revealed a refractive index of n = (1 -2.1 × 10 −5 ) at the same wavelength as the light source wavelength of the Lessmüller OCT system. Clearly, the influence of the plasma's refractive index on the OCT measurements is negligible.…”