Sensitivity of Melt Pool Size and Porosity Appearing to Base Plate Preheating in Laser Powder Bed Fusion Process

The base plate temperature ranks among the crucial building parameters whose effect on melt pool dimensions and porosity defects generation has not been sufficiently discussed in literature. In the current study, with the aim to explore the dependence between melt pool dimensions, porosity defects and base plate preheating, a 3-dimensional thermal finite element model is carried out to create IN718 single beads, at various base plate temperatures. The dimensions of the melt pool behave favourably with the base plate preheating. Indeed, the melt pool depth, width and length increase continuously with the heat of the base plate, from 20 °C to 500 °C. The melt pool width is more responsive to the base plate temperature than the melt pool depth. Numerical results also indicate that the melt dimensions become more responsive to the temperature of the base plate at a slower scan speed. The degree of porosity is predicted under multiple values of base plate temperature and the results show that porosity tends to disappear with further preheating of the base plate. A satisfying accordance between the numerical finding and the experimental results from literature is identified

Traitement des diplegies laryngees en fermeture: Apport du laser

Introduction: Les diplegies laryngees en fermeture sont rares et mal tolerees par les patients. Leur prise en charge therapeutique a connu de nombreuses avancees au cours des dernieres annees. Le but de ce travail est dfetudier la place du laser dans leur prise en charge.Malades et methodes : Notre etude est retrospective a propos de six patients porteurs de diplegie laryngee en fermeture. Lfage moyen etait de 46 ans (16 et 70 ans). Lfetiologie etait une intubation prolongee ou traumatique dans 3 cas, post thyroidectomie totale dans deux autres cas et idiopathique dans 1 cas. Le traitement a consiste en une tracheotomie en urgence dans 5 cas. Tous les patients ont beneficie dans un secondtemps dfun traitement au laser apres 9 mois de surveillance.Resultats : La cordectomie posterieure a ete realisee en premier temps dans 4 cas. Elle etait bilaterale en deux temps dans 2 cas et unilaterale dans 2 cas. Une aryteno.dectomie initiale a ete realisee pour les deux autres patients. Une revision chirurgicale a consiste en une arytenoidectomie dans 2 cas et une cordotomie partielle posterieure controlaterale dans un cas. La decanulation etait bien toleree pour 4 patients. Un seul malade a garde une gene respiratoire sans veritabledyspnee avec une canule parlante fermee et la decanulation a ete refusee. Une voix satisfaisante a ete obtenue pour tous les malades. Des fausses route transitoires ont ete note dans 2 cas.Discussion : Actuellement, le traitement endoscopique au laser constitue le traitement de choix dans la diplegie laryngee et doit etre propose en premiere intension. Deux techniques principales sont decrites :  lfaryteno.dectomie au laser type Ossof et la cordectomie posterieure transverse de kashima. plusieurs series ont defendu chacune des deux techniques. Notre serie a montre que les deux techniques peuvent etre associees pour donner de meilleurs resultats.Mots cles : diplegie laryngee, Laser, aryteno.dectomie, cordectomie posterieure

Parameters Selection for the Production of Fully Dense Metals Processed by Selective Laser Melting

Selective laser melting (SLM) presents significant assets for both industrial and academic fields. However, the process parameters selection is yet challenging. It presents tens of parameters to be carefully selected, including laser power and speed, bed thickness, hatching space, and other parameters, for the manufacturing of parts with high density. This paper provides a deeper understanding of the processing parameters’ effect on the evolution of the product’s density. A series of numerical simulations of porosity is achieved on Ansys Additive© software and it shows the evolution of the relative density at different laser powers and scan speeds. Numerical results show that low laser power and accelerated scan lead to the generation of a small melt pool, and consequently low density. In the opposite case, at high power and slow scan, the created melt pool is wide enough to avoid porosity and generate fully dense products. The product density is proportionally related to the melt pool size. Hence, it could be estimated through the correlation with the melt pool width, which enables the perfect selection of the hatching space for the selected set of parameters

Comparative Analysis of Melt Pool Evolution in Selective Laser Melting of Inconel 625 and Inconel 718 Nickel-Based Superalloys

One of the key advantages of Additive Manufacturing is the versatility in working with a wide range of materials. Among these materials, Nickel-based superalloys have drawn great attention of specialists.  This study investigates the behavior of Inconel 625 and Inconel 718 during selective laser melting. While these alloys have many similarities, thus their distinct chemical compositions determine different responses to this new process, which the authors aimed to elucidate in this study. Numerical simulations using ANSYS Additive® software were conducted to compare the melt pool dimensions (depth and width) of Inconel 625 and Inconel 718. The results reveal that the material's thermal properties play a significant role in determining the melt pool geometry. The Inconel 718 consistently exhibited larger melt pool dimensions than Inconel 625. The findings highlight the importance of understanding the connection between the material properties and process parameters

Facteurs predictifs de survenue de pharyngostome après laryngectomie totale

Objectif : Déterminer l’incidence de survenue de la fistule pharyngo-cutanée ou pharyngostome après laryngectomie totale ainsi que les facteurs prédisposants.Matériel et méthodes: C’est une étude rétrospective qui a porté sur 187 malades ayant eu une laryngectomie totale à notre département (Janvier 1985-Décembre 2007). Nous avons étudié les facteurs cliniques, histologiques, les modalités thérapeutiques ainsi que évolutives à la recherche de corrélation avec la survenue de pharyngostome après laryngectomie totale. -Résultats : Les pharyngostomes ont été observé dans14,4% des cas. La chimioradiothérapie préopératoire était significativement corrélée à l’apparition de pharyngostome (p=0,008). L’infection postopératoire est un facteur hautement significatif de survenue de pharyngostome (p=0,000). De même que l’hémorragie postopératoire (p=0,016), les troubles de ladéglutition (p=0,037), et les bronchopneumopathies (p=0,032). La rupture capsulaire lors d’un envahissement ganglionnaire était très  significativement corrélée à la survenue d’un pharyngostome (p = 0,001).Conclusion : en présence de facteurs de risque significatifs de  pharyngostome, cette complication peut ainsi être prévue même si sa prévention demeure encore difficile.Mots-clés : Pharyngostome, Laryngectomie totale, Incidence, facteurs prédisposants

Sensitivity of Melt Pool Dimensions and Keyhole to Laser Beam Diameter

The laser powder bed fusion process has witnessed a huge interest in recent years since it has the potential to produce challenging shapes in a broad range of applications. The process parameters have a considerable effect on melt pool size and on the development of defect porosity. This paper predicts numerically the effect of a large range of laser beam diameters on melt pool dimensions and on the occurrence of porosity defects such as keyhole. A series of single beads of Inconel IN625 was made using various combinations of beam diameters, scan speeds, and laser powers. The use of a large diameter was more suitable rather than a small diameter as it ensures a large and shallow heat affected zone, thus decreasing the development of the keyhole defect. Our numerical results correlate satisfactorily with experimental finding from literature

CFD Investigation on the Steady Interaction between an Offset Jet and an Oblique Wall Jet

In this paper a CFD investigation on the interaction between an offset jet and an oblique wall jet using two-dimensional steady RANS equations is performed. This combination is denoted WOJ (Wall Offset jets). Several turbulence models such as the standard k-ω, SST k-ω, standard k-ε, RNG k-ε and realizable k-ε models are tested in the present study. A parametric study is performed to highlight the wall inclination effect on the WOJ flow maximum velocity decay as well as the shear layers spreading. Comparison between combined wall and offset jet (WOJ) and single offset jet (SOJ) flows is also established. Results show that increasing the wall inclination improves the combined wall and offset jets flow spreading. Furthermore, the outer shear layers spreading, is better than the inner shear layers one. Comparing to the combined wall and offset jet flow (WOJ), a better spreading is found in the case of single offset jet flow (SOJ)

Numerical study of the Rayleigh-Bénard convection in two-dimensional cavities heated by elliptical heat sources using the lattice Boltzmann method

This study aims to investigate numerically the Rayleigh-Bénard Convection using an in-house Fortran 90 code based on the lattice Boltzmann method. The bottom wall is equipped with two hot circular/elliptical sources and the right wall is open. The non-linear coupled differential governing equations are formulated using the lattice Boltzmann equation associated with the Boussinesq approximation. The simulations are conducted for (103 ≤ Ra ≤ 106) and Pr = 0.7 (corresponding to air). The code verification showed a good reliability of the present mesoscopic numerical approach. Several configurations related to the size and shape of the heaters were studied. It was found that elliptically shaped heat sources provide higher heat transfer rates compared to circular sources