Upcoming strict CO2 regulations lead car manufacturers to look for mass saving solutions. The use of advanced high strength steel (AHSS) solutions enable optimizing both crash performances and mass saving. Particularly, the use of laser welded blanks made of dissimilar high strength steels is an efficient weight optimization solution. To support the joining of AHSS in car body design, a 3D model of heat transfer, turbulent flow and transport of species in the laser weld pool has been developed. It aims at providing a better understanding of diffusive-convective mixing in the weld and its influence on the weld mechanical properties. The presented model allows predicting the weld geometry and the element distribution. To validate the model, experimental tests were carried out. Welding of two dissimilar steels with different laser beam offset from the joint line was performed. Numerical and experimental investigations of dissimilar butt laser welding between high Mn and dual phase steels were carried out. The cross sections of the welds were characterized by scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDX) elemental analysis. Quantitative mappings of Mn distribution in the melted zone offer an overview of mixing intensity. The results of the simulation have been found in good agreement with the experimental data. To go further and to assess the effect of weld mixing on mechanical performances, tensile tests were done. It was found that tensile behavior of the welds is determined by level of Mn and C dilutions. For attaining maximal joint performances, it is necessary to comprehend the elements distribution in the melted zone and to be able to control it through an accurate choice of operational parameters.

The aim of this work is the detection of open defects in metallic materials using laser-material interaction coupled with infrared thermography. This process is a possible alternative for magnetic particles testing and dye penetrant testing in the field of non-destructive testing. In this context, a numerical simulation model is implemented with COMSOL Multiphysics®. This model allows us to look for the process optimal parameters through numerical experimental designs. It's an original work for modeling a back and forth scanning. Experimental works are also done in order to validate our numerical model and also to have reliable input data.

The success of new high-strength steels allows attaining equivalent performances with lower thicknesses and significant weight reduction. The welding of new couples of steel grades requires development and control of joining processes. Thanks to high precision and good flexibility, laser welding became one of the most used processes for joining of dissimilar welded blanks. The prediction of the local chemical composition in the weld formed between dissimilar steels in function of the welding parameters is essential because the dilution rate and the distribution of alloying elements in the melted zone determines the final tensile strength of the weld. The goal of the present study is to create and to validate a multiphysical numerical model studying the mixing of dissimilar steels in laser weld pool. A 3D modelling of heat transfer, turbulent flow and transport of species provides a better understanding of diffusion and convective mixing in laser weld pool. The present model allows predicting the weld geometry and element distribution. The model has been developed based on steady keyhole approximation and solved in quasi-stationary form in order to reduce the computation time. Turbulent flow formulation was applied to calculate velocity field. Fick law for diluted species was used to simulate the transport of alloying elements in the weld pool. To validate the model, a number of experiments have been performed: tests using pure 100μm thick Ni foils like tracer and weld between a rich and poor manganese steels. SEM-EDX analysis of chemical composition has been carried out to obtain quantitative mapping of Ni and Mn distributions in the melted zone. The results of simulations have been found in good agreement with experimental data.

Laser Welded Blank solutions enable to reduce vehicles weight and to optimize their crash performances by means of simultaneous tuning of different grades and thicknesses. The present work aims to characterize numerically and experimentally materials mixing during laser welding. For better understanding of materials mixing based on convection-diffusion process in case of full penetrated laser welding, a 3D simulation of fluid flow, heat transfer and mass transfer has been performed to provide fusion zone shape and elements distribution map. The model has been developed basing on steady keyhole approximation and solved in quasi-stationary form in order to reduce computation time. Turbulent flow model was used to calculate velocity field. Fick law for diluted species was integrated to simulate the transport of alloying elements in the weld pool. In parallel, a number of experiments using pure Ni foils as tracers have been performed to obtain mapping of Ni distribution in the melted zone. SEMEDX analysis of chemical composition has been made to map elements distribution in the melted zone. The results of simulation have been found in good agreement with experimental data.

Dissimilar laser beam welding between A5754 Al alloys and AZ31 Mg alloys with the plate thickness of 2 mm was investigated. Complex flow pattern characterized by a large volume of intermetallic compounds Al12Mg17 and Al3Mg2 is formed in the fusion zone. Microhardness measurement of the dissimilar welds presents an uneven distribution due to the complicated microstructure of the weld, and the maximum value of microhardness in the fusion zone is much higher than of the base materials.

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 chamfer geometry. It consists in simulation of heat transfer phenomena using heat equivalent source approach and implementing in finite element software COMSOL Multiphysics. A numerical exploratory designs method is used to identify the heat sources parameters in order to obtain a minimal required difference between the numerical results and the experiment which are the shape of the welded zone and the temperature evolution in different locations. The obtained results were found in good correspondence with experiment, both for melted zone shape and thermal history.

The present article is dedicated to the study of the evolution of the keyhole obtained during the drilling of samples of Zinc by YAG laser beam. Two experimental methods are used to observe the shape of the keyhole. The first one is the Direct observation of Drilled hOle, that lets to obtain the shape of the keyhole for different laser powers and different pulse durations. The observations are carried out after drilling. The second one needs to clamp the zinc sheet with a quartz glass. This glass is chosen because of its excellent thermal shock resistance and its high light transmittance. The observation of the keyhole during the drilling shape is then realized through the quartz with a high-speed CCD camera. The evolution of the shapes of the keyhole obtained by both methods lets to highlight the role of the multiple reflections on the shape of the keyhole. When multiple reflections occur, the absorption of the energy by the wall of the keyhole increases and consequently the depth of the keyhole increases. This phenomenon was verified experimentally: in the first method, the multiple reflection of the laser beam on the wall of the keyhole occurs, whereas, for the second experimental set-up, it can be considered that there is only one impact of the laser beam on the keyhole walls. This result was theoretically proved by calculating the absorption for different shapes of the keyhole, in both cases: one reflection and multiple reflections, using the ray tracing method.The present article is dedicated to the study of the evolution of the keyhole obtained during the drilling of samples of Zinc by YAG laser beam. Two experimental methods are used to observe the shape of the keyhole. The first one is the Direct observation of Drilled hOle, that lets to obtain the shape of the keyhole for different laser powers and different pulse durations. The observations are carried out after drilling. The second one needs to clamp the zinc sheet with a quartz glass. This glass is chosen because of its excellent thermal shock resistance and its high light transmittance. The observation of the keyhole during the drilling shape is then realized through the quartz with a high-speed CCD camera. The evolution of the shapes of the keyhole obtained by both methods lets to highlight the role of the multiple reflections on the shape of the keyhole. When multiple reflections occur, the absorption of the energy by the wall of the keyhole increases and consequently the depth of the keyhole increase...

Mechanical bonding and interface behaviour play a key role for any materials deposited on different substrates. Usually, a post-spray heat treatment is required to improve the coating morphology and to enhance mechanical properties of thermal-sprayed polymeric coating. The effects of YAG, CO2 and diode laser radiations on as-sprayed PEEK coating deposited on stainless steel and aluminum substrates were investigated. The results revealed a good coating densification and interface behavior. A correlation between coating and substrate absorption coefficients, their thermophysical properties and laser operating parameters was shown. Besides, the finite element modeling based on IR temperature measurements during diode laser irradiation demonstrated that the densification of organic coating occurs above its melting point.

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.

This paper presents a comparison between simulation and experimental results of the melting process of metallic material by a pulsed laser source Nd-YAG. Variations of the thermophysical properties were considered. Furthermore, the model included the effects of the surface-tension gradient on the fluid surface and the buoyancy force. The keyhole effect induced strong surface deformations and often formed cavities, which arre undesirable in the surface treatment process. An experimental study of the surface profile of the melted zones was also conducted to seek a relationship between the so-called keyhole effect and the laser triangulation measurements. The predicted Laser Melted Zone (LMZ) morphology was in good agreement with the corresponding experimental measurements for various irradiation conditions, as long as the keyhole effect did not occur.

Erratum to ‘‘Using Infrared thermography in order to compare laser and hybrid (laser+MIG) welding processes’’ [Optics & Laser Technology 41 (2009) 665–670] Simone Mattei a, , Dominique Grevey , Alexandre Mathieu , Laetitia Kirchner b a Institut Carnot de Bourgogne,UMR5209 CNRS-Universite0 de Bourgogne, IUT Le Creusot, 12 rue de la Fonderie, 71200 Le Creusot, France b EADS France, 12 rue Pasteur, 91 152 Suresnes Cedex, France

While hybrid laser welding and coating processes involve a large number of physical phenomena, it is currently impossible to predict, for a given set of influencing factors, the shape of the molten zone and the history of temperature fields inside the parts. This remains true for complex processes, such as the hybrid laser/MIG welding process, which consists in combining a laser beam with a MIG torch. The gains obtained result essentially from the synergy of the associated processes: the stability of the process, the quality of the seam realized, and the productivity are increased. This article shows how, by means of a reduced number of experiments (8), it is possible to predict the shape of the molten zone and the temperature field inside parts, for a given window of influencing factors. This method consists in combining the method of exploratory experimental designs with a numerical modelling of the thermal phenomena that occurs during the process, by using the ‘heat equivalent source” approach [1], [2], [3], [4]. Two validations of this method have been carried out: the first for a set of parameters inside the experimental design, and the other for a set of parameters that lies outside the experimental design, but inside the domain investigated.

In order to deepen the understanding of the differences between laser and laser-arc hybrid welding, comparisons were undertaken using thermography. The experiments were carried out for a T assembly of aluminium alloy plates. Modelling, based on the finite element method approach, was realized using IR temperature measurements and seam geometry. For a value of the power supply, depicted as a surface source in the hybrid case, agreement was found between simulated and measured temperatures. The arc power supply efficiency value is similar to the usually used value.

In this work, we present the study of the possibilities of the stimulated IR thermography as helps with the detection of defects of insulation in building.The process of insulation studied was selected among most representative of the French market.It is about an insulating complex made up of a plate of plaster facing on which is fixed expanded polystyrene.Among all the possible defects of insulation, we chose to study those which are most usually met in France.Thus we show that the method allows the detection of defects generated by a complete absence of insulator (filled in all or partly by plaster), defects due to the partial suppression of insulator, filled by plaster, to mask a transport of fluid and finally of defects generated by a variation thickness of insulator.

In this work, we present the study of the possibilities of the stimulated IR thermography as helps with the detection of defects of insulation in building. The process of insulation studied was selected among most representative of the French market. It is about an insulating complex made up of a plate of plaster facing on which is fixed expanded polystyrene. Among all the possible defects of insulation, we chose to study those which are most usually met in France. Thus we show that the method allows the detection of defects generated by a complete absence of insulator (filled in all or partly by plaster), defects due to the partial suppression of insulator, filled by plaster, to mask a transport of fluid and finally of defects generated by a variation thickness of insulator.

The purpose of the present study is to estimate the weldability of a polymeric material couple according to their thermal and optical properties. A first model based on Mie theory and Monte Carlo method describes the laser beam behavior in semi-transparent media and makes it possible to approximate the laser power distribution at the interface of the two materials. A second model based on finite element method permits the temperature field estimation into both parts to be welded. The results are validated by infrared thermography.

Welding laser modelling requires knowledge about relative changes of many thermo-physical parameters involved in the interaction. The absorptivity of the material is one of the most important. In this study, experimental measurements of absorptivity with an integrating sphere on two alloys (aluminium and magnesium) were made. These results were compared with an analytical calculation that takes into account the trapping of the beam by multiple reflections inside the keyhole. Based on a statistical method, an empirical law is proposed connecting absorptivity with the peak power of the laser and the duration of interaction. During the interaction, two distinct phenomenologies are brought to light. A threshold is then defined after which the physical process becomes stable. Below this threshold, the measurement of absorptivity is problematic, and the values are widely dispersed.

In this paper a numerical model for laser beam scattering in the semi-transparent polymers is presented, using a Monte Carlo algorithm and the Mie theory. The algorithm correctly accounts for the independent multiply-scattered light. We describe the algorithm, present a number of important parameters that account in the welding process, and explicitly show how the algorithm can be used to estimate the laser beam intensity both inside the semi-transparent component and at the welding interface and the beam widening. For the model validation an experimental bench test has been realized and some results from two test cases are presented.