Dominique Grevey

Continuous wave Nd:YAG laser cladding modeling: A physical study of track creation during low power processing

This paper concerns the modeling of cladding using an Nd:YAG laser operating at low powers typically less than 800 W. Experimental observation of the evolution of the mass of the clads shows two power thresholds. The theoretical study relies on a calculation of the fluence provided to the substrate and on a model of heat transfer into the substrate. We suggest that the first threshold is the power required for substrate melting. The second power is the threshold when the powder is directly melted by the beam and is therefore a liquid when contacting the substrate.

Experimental design approach to optimize selective laser melting of martensitic 17‐4 PH powder: part I – single laser tracks and first layer

Purpose – The purpose of this paper is to investigate the effect of main process parameters of selective laser melting (SLM) technology on single lines and single layers manufactured from 17‐4 PH martensitic powder using the experimental design approach.Design/methodology/approach – A fractional factorial approach has been applied to vary and to identify the optimal set of process parameters using three different powder particle size distributions for 17‐4 PH steel. This paper assesses the impact of influence factors such as process and material parameters on objective factors such as dimension of single lines and single layers, as well as surface roughness.Findings – The influence of process parameters and materials properties on single line and single layer manufacture is shown and proved statistically. The effect of each process parameter and their interactions on single layer and single line stability and quality has been investigated, and a complex objective function analyzing geometrical stability o...

Diode laser welding of ABS: Experiments and process modeling

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 important insights concerning the fundamental phenomena that govern the process could be extracted. This approach proved to be an efficient tool in determining the weldability of polimeric materials and assures a significant reduction of time and costs with the experimental exploration.

Comparison of the performance obtained with a YAG laser cutting according to the source operation mode

Abstract In this paper, the cutting performance of continuous and pulsed YAG laser equipment is compared. Cutting tests were carried out on plates from car frames, both coated and uncoated. Results are analysed in terms of the energy supplied by the source per volume of treated material. It appears that continuous equipment offers a better performance as regards operating speed, pulsed sources being penalized mainly by their low filling rate. A good quality beam producing a small laser spot gives a high scanning speed.

MoSi2 laser cladding—a comparison between two experimental procedures: Mo–Si online combination and direct use of MoSi2

Abstract 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, MoSi 2 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 MoSi 2 powder.

MoSi2 laser cladding—A new experimental procedure: double-sided injection of MoSi2 and ZrO2

Abstract 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 MoSi 2 . 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 MoSi 2 layer synthesized using laser beam is the layer fragility. To avoid this fragility, unstabilized zirconia was employed in many cases. The paper presents the reasons, the set-up and the results of a new powder injection technique that uses two powders (MoSi 2 and ZrO 2 ) to produce the cladding using a Nd:YAG cw laser beam.

MoSi2 laser cladding—elaboration, characterisation and addition of non-stabilized ZrO2 powder particles

Abstract The cladding process using laser beam radiation comprises different operational regimes, depending on the involved lasers (usually CO 2 or Nd:YAG) and materials. A series of experiments has been carried out to investigate Nd:YAG laser cladding using MoSi 2 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 MoSi 2 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 consists in crack reduction (ideally elimination) and to reach that we have considered the addition of components that can create opposing stresses during solidification, like non-stabilized Zirconia powder particles. The results of these experiments are also widely presented in the paper.

Characterisation of cw Nd : YAG laser keyhole dynamics

Abstract The paper concerns laser–matter interaction characterisation. In this work, we use a rapid CCD camera located coaxially to the laser beam and we compare recorded images with those obtained by numerical modelling. Because images are difficult to understand, we compute thermal radiation emitted by a keyhole of fixed geometry and we adjust it trying to approach the camera record. The modelling treats radiative heat transfer within the keyhole and determines the sensor illumination map. By adjusting the geometrical characteristics of the hole, we seek to obtain the image that corresponds as well as possible to the realised experiment. Results are compared with other experimental methods simultaneously performed plume characterisation with an electric probe and spectrometric analysis. They show the existence of two distinct behaviours of the keyhole: a pseudo-steady state associated with regular and pseudo-constant keyhole shapes, low frequencies of electric current in the plume, and generally good welding results, and a highly dynamic mode associated with irregular and rapidly varying keyhole shapes, high frequencies in the plume current and generally poor welding results.

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...

Numerical investigation of laser beam shaping for heat transfer control in laser processing

This article presents a thermal finite volume model adapted to investigate laser processes. It is specially developed to treat moving heat sources with phase changes, melting and vapourisation. Heat transfer control in laser processing is particularly useful when processes must respect prescribed temperatures, or more generally, prescribed constraints. These processes involve generally several laser sources, or non-conventional power distribution. Hence, they have numerous parameters to set. Experimental optimisation is difficult and may be expansive. The numerical model is a useful and cheaper tool for development of those complex processes. For example in this article, two special laser processes are investigated: control of high carbon steel welded line cooling, zinc-coated sheets lap welding.