A three-dimensional (3D) transient model of a transferred argon arc in interaction with an anode material is presented and the results discussed. The model based on a finite volume method is developed using the open software @Saturne distributed by Electricite de France. The 3D model includes the characterization of the plasma gas and of the work piece with a current continuity resolution in the whole domain. Transport and thermodynamic properties are dependent on the local temperature and on the vapours emitted by the eroded material due to the heat flux transferred by the plasma. Drag force, Marangoni force, Laplace and gravity forces are taken into account on the weld pool description. The plasma and the weld pool characteristics are presented and compared with experimental and theoretical results from the literature. For a distance between the two electrodes of d = 5 mm and an applied current intensity of I = 200 A, the vapour concentration is weak. The influence of the parameters used in the Marangoni formulation is highlighted. Finally, in agreement with some authors, we show with this global transient 3D model that it is not necessary to include the voltage drop in the energy balance.

http://iopscience.iop.org/article/10.1088/0022-3727/46/13/135206/pdf

Plasma–weld pool interaction in tungsten inert-gas configuration

This paper presents a vision-based approach for wire extension measurement and melt pool detection. The image analysis applies on the image sequences, which are extracted from a recorded welding video. The algorithms have been developed using the image processing combining profile analysis, intensity thresholding, region growing, filtering, and morphology. The goal is to use these computed parameters to help in welding control and defect examination. The software runs automatically and has been verified on various videos from different welding experiments. The resulting data are also represented and compared with chronological knowledge to improve the reliability of the system.

Vision-based control of wire extension in GMA welding

Conventional methods used to inspect the molten pool surface induced by arc welding processes are based on post-welding evaluation using destructive or semi-destructive testing methods. Many attempts were performed to develop alternative and nondestructive tests. In this context, a polarimetric vision methodology is evaluated. The polarimetric parameters are measured from the thermal radiations emitted by the hot liquid metal at a wavelength within an arc plasma blind spectral window. The Stokes parameters and their segmentation within a Gaussian mixture model allow to discriminate artifacts at the surface of the liquid metal. After weld pool solidification, the use of scanning electron microscopy and energy dispersive spectroscopy allow to identify the artifacts, i.e., floating alumina particles.

Polarimetric imaging method for surface quality evaluation of a liquid metal pool obtained during welding

During tungsten inert gas (TIG) welding process, heat transfer between plasma and the work piece leads to a metallic weld pool. Combination of different forces produces movements on the molten pool surface. Following the predominance of the forces, the depth and width of the weld pool differ, affecting the weld quality. One of our aims is to observe the flow motion applying different experimental conditions and nature of materials. This provides a set of observations that allows us to quantify the velocity, the weld pool shape, and dimensions. These quantities are essential to validate numerical models used to adjust TIG parameters. In this paper, visualization of an AISI 304L stainless steel molten pool with high-speed imaging, velocity estimation, and microscopic observation are presented.

High-Speed Camera on Molten Pool in Transferred Arc Configuration

The nature and detailed behaviour of slag islands in ferritic stainless steel welds have been analysed via weld pool video imaging, welding parameter monitoring, scanning electron microscopy, and in situ optical emission spectroscopy. The aim of the investigation was to understand how changes in weldability in 31 commercial very low-sulphur steels of EN 1.4509 (“441”, S43940) can be attributed to in situ slagging phenomena. The results showed that three slagging mechanisms can co-exist and alter the properties of the weld pool. Very stable, up to O 3 mm, aluminium-based, titanium-containing glassy films were observed directly underneath the welding arc in steels with excessive aluminium deoxidation. Such films could occasionally maintain their stability throughout the weld cycle. Steels with excessive aluminium deoxidation also showed stable, <O 1 mm, calcium-aluminium-titanium clusters in various places along the weld pool, occasionally on the glassy films, if present. Sudden movement of these clusters to the fusion line led to an irregular fusion line and abrupt changes in the fluid flow. In low-aluminium steels, the majority of slags were rich in calcium and titanium and they accumulated to the rear of the weld pool. Various build-up and breakdown mechanisms of slagging are discussed.

Behaviour and influence of slag islands in ferritic stainless steel welds

: Surface flow visualization of Gas Tungsten Arc weld pools for HY-80 steel is presented using a pulsed laser light source and a conventional night vision image-intensifier tube equipped video camera. Visualization of the weld pool free surface is made possible by seeding a flow with alumina particles for both stationary and moving arc welds. These visualizations reveal several new features not incorporated in the existing models for stationary welds. A strong clockwise stirring is observed contrary to the axi symmetric computational models. Also, the pool surface shows a bulge near the center. Complex flow patterns are observed for moving arc welding. Interpretations of the observed flows based on the driving forces are provided.

Daniel C. Espinosa

Papers

Visualization of gas tungsten arc weld pools