Explanation of penetration depth variation during laser welding under variable ambient pressure

Abstract

Science Arts & Métiers (SAM)is an open access repository that collects the work of Arts et Métiers ParisTech researchers and makes it freely available over the web where possible. It has been observed that the penetration depth during laser welding (LW) under vacuum or reduced ambient pressure could be significantly greater than that during welding under atmospheric pressure. Previous explanations of this phenomenon usually limit to specific wavelength laser welding and have difficulties in explaining why the variation will disappear, as the welding speed increases. Here, we propose that this variation is caused by the temperature difference of keyhole wall under variable ambient pressure based on a correct physical description of related processes.A new surface pressure model, dependent on ambient pressure, is proposed for describing the evaporation process during laser material interaction under variable ambient pressure. For laser welding of a 304 stainless steel with 2.0 kW laser power and 3 m/min welding speed, it is shown that the average keyhole wall temperature is around 2900 K under atmospheric pressure, and only around 2300 K under vacuum, which results in significant penetration depth variations. Interestingly, it is also shown that as the welding speed increases, the average temperature of the front keyhole wall gradually rises due to the reduction of the mean incident angle of laser, and the magnitude of this increase is larger in welding under vacuum than under atmospheric pressure. It allows us to explain why the penetration depth improvement decreases to zero with the increase of welding speed.

3D transient multiphase model for keyhole, vapor plume, and weld pool dynamics in laser welding including the ambient pressure effect

“…However, recent research [19,23] showed that the evaporation process is actually influenced by recoil pressure and ambient pressure. Therefore, an improved recoil pressure model dependent on ambient pressure, called a surface pressure model and developed by Pang et al [23], is used to describe the evaporation process in laser welding. The surface pressure model can be described as follows [23]:…”

“…Therefore, an improved recoil pressure model dependent on ambient pressure, called a surface pressure model and developed by Pang et al [23], is used to describe the evaporation process in laser welding. The surface pressure model can be described as follows [23]:…”

“…The parameters of the surface pressure model for laser welding of stainless steel under atmospheric pressure are referred to in [23].…”

[INVITED] An overview of the state of art in laser welding simulation

“…Neglecting it, the user simulates in fact welding under vacuum conditions and at the very beginning, the keyhole tends to appear before the vaporization temperature [31]. In the literature, authors like Pang et al [57,58] have treated this effect with particular caution in complete simulations. They have shown that the recoil pressure p rec is equal to the ambiant one p amb for a surface temperature smaller than the evaporation temperature corresponding to this ambiant pressure; For temperatures greater than this evaporation temperature, the recoil pressure is then defined by p 1 /2 sat r β ( + ) .…”

Laser Welding under Vacuum: A Review

“…Pang et al [23,57,58] investigated the physical phenomenon of laser welding under vacuum by numerical simulation. Based on the 3D transient multiphase model of laser welding, an improved model of recoil pressure for laser welding under any ambient pressure was proposed.…”