Alexandre Mathieu

Characterizing weld pool surfaces from polarization state of thermal emissions

In this Letter, a vision-based remote sensing methodology is proposed to measure the topography of weld pool surfaces from one single view. Thermal radiations emitted by the hot liquid metal at a wavelength within the arc plasma blind spectral window are acquired by a wavefront division polarimetric system. The refractive index of the liquid metal and the topography of the weld pool surface are inferred from the polarimetric state of the thermal radiations.

Laser brazing of steel-aluminum assembly

New anti-pollution and energy saving laws impose reduction of fuel consumption for vehicles of the automotive industry. This reduction may be provided through the lightening of vehicles by introducing Aluminum parts into the Steel car-body. Laser-brazing represents an adequate process than can be used to realize this kind of new structure. The main problem with thermal joining processes is the formation of inter-metallic phases which decreases the ductility of the joint. Laser-brazing allows a localized fusion which limits the development of brittle phases. This paper presents the results of a feasibility study for different joining-configurations with different filler materials: an Aluminum based alloy and a Zinc based alloy. The study shows that using zinc alloy for filler material gives better mechanical performances. Simultaneously, observations by optical and electron microscopy were carried out to characterize the joints. In order to understand the influence of the temperature on the formation of inter-metallic phases, a thermal modeling by FEM of the process was also carried out.New anti-pollution and energy saving laws impose reduction of fuel consumption for vehicles of the automotive industry. This reduction may be provided through the lightening of vehicles by introducing Aluminum parts into the Steel car-body. Laser-brazing represents an adequate process than can be used to realize this kind of new structure. The main problem with thermal joining processes is the formation of inter-metallic phases which decreases the ductility of the joint. Laser-brazing allows a localized fusion which limits the development of brittle phases. This paper presents the results of a feasibility study for different joining-configurations with different filler materials: an Aluminum based alloy and a Zinc based alloy. The study shows that using zinc alloy for filler material gives better mechanical performances. Simultaneously, observations by optical and electron microscopy were carried out to characterize the joints. In order to understand the influence of the temperature on the formation of in...

Weld pool surface temperature measurement from polarization state of thermal emission

This paper presents a passive polarimetry method using a division of aperture optical device in order to measure the temperature distribution at the weld pool surface. Thermal emission from a hot liquid metal was investigated at a near-infrared wavelength corresponding to a blind spectral window of a helium plasma generated during gas tungsten arc welding process. The refractive index of liquid metal and the surface radiance are deduced from the polarisation state of thermal emissions. Based upon the knowledge of both characteristics, the temperature distribution can be calculated.

Plasma effect on weld pool surface reconstruction by shape-from-polarization analysis

The polarimetric state of the thermal radiations emitted by the weld metal contains geometric information about the emitting surface. Even though the analysed thermal radiation has a wavelength corresponding to a blind spectral window of the arc plasma, the physical presence of the arc plasma itself interferes with the rays radiated by the weld pool surface before attaining the polarimeter, thus modifying the geometric information transported by the ray. In the present work, the effect of the arc plasma-surrounding zone on the polarimetric state and propagation direction of the radiated ray is analyzed. The interaction with the arc plasma zone induces a drop in ray intensity and a refraction of ray optical path.

Laser braze welding using hot (88%-aluminum,12%-silicon) filler material to join steel with aluminum

New anti-pollution and energy-saving regulations will require the automobile industry to reduce the rate of fuel consumption per vehicle. Part of the solution could be to make car bodies lighter, which can be achieved by introducing some aluminum parts in place of steel. Laser braze welding is an appropriate method for realizing such structures. The main problem in thermal joining processes is the formation of intermetallic phases, which are detrimental to the mechanical performance of the joint. Laser brazing localizes the fusion and inhibits the development of brittle phases. Another problem encountered in brazing is poor wetting of the liquid material on the sheet-joint surface. This problem is often solved by the use of a brazing chemical flux or by working in a controlled atmosphere or vacuum. In an industrial context, however, such techniques are very difficult to implement. This paper presents the results of joining a 6016 aluminum alloy with hot dip galvanized low carbon steel using an aluminum-based filler material. This study demonstrates that the use of a chemical flux is not necessary. In order to improve the mechanical performance of the joint, the use of a hot wire, rather than a chemical brazing flux, appears a good solution. Optical and scanning electron microscopy was employed to characterize the joints. The temperature of the wire, just before illumination by the laser beam, was measured with a pyrometric device. It was found that preheating the wire has a strong influence on the mechanical properties of the joints.New anti-pollution and energy-saving regulations will require the automobile industry to reduce the rate of fuel consumption per vehicle. Part of the solution could be to make car bodies lighter, which can be achieved by introducing some aluminum parts in place of steel. Laser braze welding is an appropriate method for realizing such structures. The main problem in thermal joining processes is the formation of intermetallic phases, which are detrimental to the mechanical performance of the joint. Laser brazing localizes the fusion and inhibits the development of brittle phases. Another problem encountered in brazing is poor wetting of the liquid material on the sheet-joint surface. This problem is often solved by the use of a brazing chemical flux or by working in a controlled atmosphere or vacuum. In an industrial context, however, such techniques are very difficult to implement. This paper presents the results of joining a 6016 aluminum alloy with hot dip galvanized low carbon steel using an aluminum-ba...

The numerical simulation of heat transfer during a hybrid laser-MIG welding of duplex steel

The present study is dedicated to the numerical simulation of an industrial case of hybrid laser-MIG welding of high thickness duplex steel UR2507Cu with Y-shaped gap geometry. It consists on stimulating the heat transfer during the welding by COMSOL Multiphysics software using heat equivalent source approach. A numerical exploratory designs method is used to identify and to optimize the heat sources parameters in order to obtain a small relative error between the numerical results and the experiment.