0000000000067111
AUTHOR
Eugen Cicala
Optimisation of refractory coatings realised with cored wire addition using a high-power diode laser
Laser; Cladding; Refractory alloys; Factorial experiments; International audience; The objective or our research was to obtain refractory alloys using the high-power diode laser (HPDL) coating technique. After optimisation using factorial experiments, two different cladding regimes were clearly distinguished. It was also shown that a very narrow transition zone exists between the two regimes, and, inside this zone, clad layers having a satisfactory compromise between the response functions (surface aspect and cavity presence) were obtained. The main objective of our study, namely, the control of the operating parameters (geometrical and kinematical) to realise adequate coatings, without cav…
Hot cracking in Al–Mg–Si alloy laser welding – operating parameters and their effects
Abstract Hot cracking is a phenomenon that frequently occurs in the laser welding of some “special” alloys, such as the aluminium–magnesium–silicon type. Each occurrence of this phenomenon needs to be studied in itself, taking into account not only the individual, but also the interactive, influences of the various parameters. The advantage of using laser beams in welding processes lies in the speeds that can be reached. The disadvantage, however, is that, owing to the high cooling rates characteristic of the interaction between the laser beam and the material, the welding speed itself becomes a cause of hot cracking. The aim of this paper is to see how this disadvantage may be eliminated. …
Diode laser welding of ABS: Experiments and process modeling
International audience; The laser beam weldability of acrylonitrile/butadiene/styrene (ABS) plates is determined by combining both experimental and theoretical aspects. In modeling the process, an optical model is used to determine how the laser beam is attenuated by the first material and to obtain the laser beam profile at the interface. Using this information as the input data to a thermal model, the evolution of the temperature field within the two components can be estimated. The thermal model is based on the first principles of heat transfer and utilizes the temperature variation laws of material properties. Corroborating the numerical results with the experimental results, some impor…
Laser-assisted narrow gap arc welding of an 18MND5 steel thick plate
Abstract Narrow gap arc welding is a common solution for the welding of thick structures. In this study, a defocused laser beam is used to pre-melt the narrow gap walls in front of an arc-welding bath. Such a welding configuration can be referred to a hybrid welding configuration. In the present work, a particular attention is given to evaluation of the interaction between an arc plasma and a defocused laser beam. High-speed imaging of the metal transfer through arc plasma is achieved thanks to a diode laser illumination system. Electrical arc parameters are logged, synchronously, in order to perform a correlation analysis and to make a diagnosis of the interaction level between laser beam …
La compréhension et la maîtrise des jonctions hétérogènes titane-aluminium réalisés par faisceau laser
La presente etude est dediee a la comprehension des facteurs influencant la resistance mecanique d’un assemblage entre l’alliage de titane Ti6Al4V avec l’alliage d’aluminium AA5754 par faisceau laser Yb:YAG. Le plan d’experiences propose a permis de mettre en evidence les effets des parametres operatoires sur la composition et la morphologie de la zone fondue ainsi que l’identification des conditions operatoires les plus favorables. L’etude numerique multiphysique basee sur l’utilisation de la methode des elements finis prenant en compte les transferts de chaleur, la mecanique des fluides et le transport des especes, a demontre les consequences des differences de proprietes thermo-physiques…
Direct laser welding of pure titanium to austenitic stainless steel
Abstract Direct butt joining of pure titanium to 316L stainless steel with continuous Yb:YAG laser was performed with variation of the beam offset from joint line. Mechanical properties of samples were evaluated by tensile tests and three-point flexural tests. The fractured surfaces and cross sections of welds were examined by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). Tensile properties of welds were strongly determined by the beam offset from joint line and are well described by Weibull statistics. Ultimate tensile strength of 174 ± 69 MPa and ultimate flexural strength of 297 ± 48 MPa were obtained. Brittle fracture took place in…
The application of the random balance method in laser machining of metals
International audience; Features peculiar to laser technology offer some advantages over more traditional processes, but, like all processes, it has its limitations. This article studies the limitations of laser machining of metals, and quantifies, through an experimental design method, the influence of operating parameters on productivity and on the quality of the machined surface. Three study materials were used: an aluminium alloy, stainless steel and a titanium alloy. An initial reading of the results indicates that productivity depends mainly on the frequency of the laser pulse and that the aluminium alloy behaves differently from the other two. The quality of the machined surface, jud…
Mechanical properties and microstructural study of homogeneous and heterogeneous laser welds in α, β,and α + β titanium alloys
International audience; Heterogeneous welding has been investigated for three different couples of titanium alloys: α/α + β, α/β,andα + β/β. Plates of 100 × 60 mm and 1.6 or 1.8 mm thick were welded with a Yb:YAG laser. Tensile tests show that the resistance of the heterogeneous welded specimens was generally controlled by those of the weakest material except for the α + β/β where the ultimate tensile strength was approximately equal to the average value of both materials. In every case, the elongation of the welded sample was found to be smaller than that of the base metals. The rupture generally took place outside the weld metal and was found to be most of the time located in the alloy ha…
MoSi2 laser cladding—A new experimental procedure: double-sided injection of MoSi2 and ZrO2
International audience; In the last decade, development of low density advanced material systems for service at temperatures up to 1300 °C was one of the goals of many researches. This kind of material should mainly have moderate fracture toughness and should exhibit oxidation resistant behaviour at low and intermediate temperature. One of the most studied materials continues to be the intermetallic compound MoSi2. The molybdenum disilicide has been considered as an attractive candidate due to its melting point (2030 °C) and excellent oxidation resistance at high temperatures. The main problem associated with the MoSi2 layer synthesized using laser beam is the layer fragility. To avoid this…
Grooving by Nd:YAG laser treatment
Abstract The properties of the laser beam have been used to produce deep and thin grooves in metals, melted material being removed with the assistance of a high velocity gas. Preliminary experiments show that the geometry and the location of the gas inlet tube are the main parameters governing the evacuation of the scoria. The influence of the nature of the materials on the depth of the grooves is discussed from examination of the grooves realized on various metals (copper, aluminum, titanium,…). Finally, a statistical study is performed to indicate the parameters that have to be controlled to secure regular grooves. It appears that the groove width is not too much affected by parameter var…
MoSi2 laser cladding—a comparison between two experimental procedures: Mo–Si online combination and direct use of MoSi2
International audience; There are very strong interests in developing low density advanced material systems for service at temperatures up to 1300°C. These materials should mainly have moderate fracture toughness at low and intermediate temperatures and should exhibit oxidation resistant behaviour. The intermetallic compound, MoSi2 has been considered to be an attractive candidate due to its melting point (2030°C) and excellent oxidation resistance at high temperatures. In this paper, we compare the results obtained with two different techniques for laser cladding, one using an online combination between Mo and Si powders, the second using direct injection of the MoSi2 powder.
Determination of an empirical law of aluminium and magnesium alloys absorption coefficient during Nd :YAG laser interaction
International audience; 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 phenomen…
Aluminum to titanium laser welding-brazing in V-shaped grooveI
International audience; Laser assisted joining of AA5754 aluminum alloy to T40 titanium with use of Al-Si filler wires was carried out. Continuous Yb:YAG laser beam was shaped into double spot tandem and defocalized to cover larger interaction zone in V shaped groove. Experimental design method was applied to study the influence of operational parameters on the tensile properties of the joints. Microstructure examination and fractography study were carried out to understand the relation between local phase content and fracture mode.Within defined window of operational parameters, statistically important factors that influenced the strength of T40 to AA5754 joints in V groove configuration w…
Experimental design method to the weld bead geometry optimization for hybrid laser-MAG welding in a narrow chamfer configuration
International audience; The work presented in this paper relates to the optimization of operating parameters of the welding by the experimental design approach. The welding process used is the hybrid laser-MAG welding, which consists in combining a laser beam with an MAG torch, to increase the productivity and reliability of the chamfer filling operation in several passes over the entire height of the chamfer. Each pass, providing 2 mm deposited metal and must provide sufficient lateral penetration of about 0.2 mm. The experimental design method has been used in order to estimate the operating parameters effects and their interactions on the lateral penetration on one hand, and to provide a…
Characterization of Fusion Lines Obtained with Laser Welding on Ductile Iron Plates
This paper studies the ductile iron (DI) weldability using laser welding. For performing an Yb:YAG continuous laser was used, with a maximum power of 6 kW. The parametrical window power (P) - welding speed (S) was explored by carrying out the fusion lines on ductile iron plates without preheating, to determinate areas of weldability (complete penetration, correct geometry) to allow further characterization. The criteria for selection of focus areas were the geometry of the fusion lines and the absence of the welding defects. The unsatisfactory domains were characterized by: collapse of the melted metal, incomplete penetration, low fusion lines quality (geometry, compactness). In present stu…
On the mechanisms involved in the tensile strength of a dissimilar Ti6Al4V/316L laser welded assembly
International audience; The aim of the present work is to analyze the thermomechanical behavior of dissimilar laser seams by means of FE modeling. The case of a Ti6Al4V/316L assembly with vanadium insert was considered. Effective mechanical properties of the main materials and cords were first estimated from NHT measurements. Modeling of the double pass laser welding process was performed first by considering shrinking of the two weld seams during manufacturing, to get the residual stress state in the welded assembly. Modeling of the tensile test was performed in a second step to study the assembly behavior during loading. In these modeling results, the mesh was the cross-section of the mic…
MoSi2 laser cladding—elaboration, characterisation and addition of non-stabilized ZrO2 powder particles
International audience; The cladding process using laser beam radiation comprises different operational regimes, depending on the involved lasers (usually CO2 or Nd:YAG) and materials. A series of experiments has been carried out to investigate Nd:YAG laser cladding using MoSi2 powder. Procedures and operating parameters for producing clad layers has been developed and their properties evaluated. The feasibility of the laser cladding technique, using a high power Nd:YAG laser, by projecting MoSi2 powder on steel substrate was demonstrated. The results indicate a low density of cracks, elevated powder catchment efficiency (between 65 and 90%) and hardness values around 1200–1300 HV. Our goal…
Microstructure and property of titanium heterogeneous laser welding
International audience; Dissimilar welding has been investigated for three different couples of titanium alloys: α/α+β, α/β and α+ββp. Plates of 100 x 60 x 1.6 or 1.8 mm were welded with a Yb: YAG laser. Tensile tests show that the properties of the dissimilar welded specimens were generally controlled by Those of the weakest material except for the α+β/β where the ultimate tensile strength was approximately equal to the average value of both materials. In every case, the welding sample elongation was found to be smaller than that of the base metals. The rupture took place away from the bead and was found to be always located in the alloy having the lowest mechanical properties. Nevertheles…
Optimisation of TA6V alloy surface laser texturing using an experimental design approach
International audience; Active surfaces of plastic injection moulds are nowadays textured using classical techniques (chemical etching or EDM). Replacement of these technologies by a laser technology introduces a big flexibility: absence of mechanical contact with the tool, decrease of the effluent's volume and a big machining precision, even in the case of the complex forms as injection moulds for example. This paper reports the experimental study of the surface laser texturing of TA6V alloy. The influence of the operating factors on the laser texturing process has been studied using two experimental approaches: Taguchi methodology and response surface methodology (RSM). Empirical models h…
The use of exploratory experimental designs combined with thermal numerical modelling to obtain a predictive tool for hybrid laser/MIG welding and coating processes
Abstract 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 th…
The numerical simulation of heat transfer during a hybrid laser–MIG welding using equivalent heat source approach
International audience; 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 …
Use of pure vanadium and niobium/copper inserts for laser welding of titanium to stainless steel
Abstract Niobium and vanadium have high metallurgical compatibility with titanium and therefore can be used as inserts to avoid the accumulation of brittle intermetallic phases such as Fe2Ti during the fusion welding of titanium alloys with steels. In the present study, the continuous double pass welding of 1 mm thick Ti-6Al-4V alloy and 316 L stainless steel plates through several mm wide pure vanadium or niobium insert was studied. In case of a vanadium insert, a beam offset on the vanadium was found to produce cold crack formation in vanadium/316 L melted zones containing more than 40 wt.% V despite the absence of σ phase. Whereas a centered beam position and offset on the steel side pro…
Gas protection optimization during Nd:YAG laser welding
International audience; Many laser processes, such as welding or surface treatments are associated with an undesired phenomenon, which is oxidation. The solution commonly employed to solve this problem approaches the shielding gas and/or the shielding gas device. What we propose in this paper is a methodology with the goal to optimize the protection gas device design as well as the gas flow in the case of laser welding and surface treatments. The pressure created by the gas flow on the sample surface is recorded and analysed together with the operating parameters influence in order to reach the objectives. The nozzle system designed and presented below assures the protection against materia…