Effect of Local Gas Flow in Full Penetration Laser Beam Welding with High Welding Speeds

Abstract

Spatter formation is a major issue in deep penetration welding with solid-state lasers at high welding speeds above 8 m/min. In order to limit spatter formation, the use of local gas flows represents a technically feasible solution. By using the gas flow, the pressure balance inside the keyhole, and therefore the keyhole stability, is affected. Existing investigations demonstrate a reduction in spatter and pore formation for partial penetration welding up to a welding speed of 5 m/min. However, the effect of the gas flow is not yet clarified for full penetration welding at welding speeds above 8 m/min. By using a precisely adjustable shielding gas supply, the effect of a local gas flow of argon was characterized by welding stainless steel AISI304 (1.4301/X5CrNi18-10). The influence of the gas flow on the melt pool dynamics and spatter formation was recorded by means of high-speed videography and subsequently analyzed by image processing. Schlieren videography was used to visualize the forming flow flied. By the use of the gas, a change in melt pool dynamics and gas flow conditions was observed, correlating to a reduction in loss of mass up to 70%. Based on the investigations, a model of the acting effect mechanism was given.

Interaction between Local Shielding Gas Supply and Laser Spot Size on Spatter Formation in Laser Beam Welding of AISI 304

“…Probably, the higher momentum transfer of the gas flow accelerated the metal vapor flow. A modified flow of the metal vapor was already shown in [38]. The increased metal vapor flow outweighed the increase of surface tension due to the protective gas and accelerated the spatters.…”

“…For welding speeds ≤5 m/min the melt flow was stabilized due to the gas flow and spatter ejections were completely suppressed [31]. Recent investigations obtained a loss of mass reduction of up to 91% with an argon gas flow under low flow rates (≤4.8 L/min) [32]. In addition, the geometry of the keyhole was affected for partial [33] and full penetration welding [34] and for the welding of lap joints [35].…”

“…The influence of the gas flow on the pressure balance in the keyhole was estimated in [33] combining investigations in [36,37]. Also, in [38] the gas flow was mentioned as a mechanism to stabilize the keyhole and to reduce spatter formation. Humps appeared at the weld seam due to the increased momentum transfer from gas flow to melt pool at flow rates ≥6.4 L/min.…”

“…Robertson et al demonstrated that material ejections could be comparatively low even at high oscillation amplitudes [22]. For the use of a local gas flow, a similar keyhole oscillation frequency but an increased keyhole oscillation amplitude were determined in comparison to the reference process without gas flow [38].…”

The influence of plasma arc composite laser welding parameters on aluminum alloy weld seam weld penetration

“…Burning or evaporation of alloying elements changes the chemical composition of the weld. Mechanical properties of the weld are difficult to control, especially when welding dissimilar non-ferrous metals is more significant [1] .…”