ACTA METALLURGICA SLOVACA 2020, VOL. 26, NO. 1, 7-10 7 DOI: 10.36547/ams.26.1.525 RESEARCH PAPER MODELLING OF LASER POWDER BED FUSION PROCESS FOR DIFFERENT TYPE MATERIALS Maria Rita Ridolfi 1 , Paolo Folgarait 1, Andrea Di Schino 2 1 Seamthesis Srl, Piacenza, Italy 2) Università degli Studi di Perugia, Dipartimento di Ingegneria, Perugia, Italy *Corresponding author: andrea.dischino@unipg.it, Università degli Studi di Perugia, Dipartimento di Ingegneria, Via G. Duranti 93, 06125 Perugia, Italy Received: 09.03.2020 Accepted: 10.03.2020 ABSTRACT The main problematic coming from the Laser Powder Bed Fusion (L-PBF) technique is the achievement of a fully dense part out of the interconnected tracks. The correct choice of process parameters is of fundamental importance to obtain a porosity free component. In this work, a model is described as able to simulate the printing process. The proposed model is a simplified numerical tool for designing processing windows suitable for metal alloys of any composition. The considered approach makes the model used as much practical as possible while keeping the physical description representative. The model is validated fitting experimental measures of track width, depth and cross-sectional area taken from three literature sources, referring to Ti6Al4V, Inconel 625 and Al7050. Effective liquid pool thermal conductivity, laser absorptivity and depth of application of laser energy are here considered as fitting parameters. Laser absorptivity and depth of application of laser energy result to rise almost linearly with increasing specific energy; the slopes of the three analyzed alloys result very close to each other. The obtained results give confidence about the possibility of using the model as a predicting tool after further calibration on a wider range of metal alloys. Keywords: selective laser melting; additive manufacturing; modelling INTRODUCTION Laser Powder Bed Fusion (L-PBF) is one of the most adopted and successful powder bed fusion-based additive manufacturing technologies for many types of alloys including stainless steels and light alloys [1-6]. In L-PBF melting and solidification of a small powder, the volume is obtained using scanning on a powder layer by a laser. In the end, the partially overlapping tracks solidified or partially re-melted on any single layer are connected and the final component is manufactured. Main critical issues coming from this method concern the achievement of a fully dense part out of tracks interconnections. The target mechanical properties of a component (e.g. strength, ductility, creep and fatigue behaviours) strongly depend on the presence of porosities [7-18]. It is well known that process parameter correct determination a key issue to achieve porosity-free manufacture. It is also known that it strongly depends on powder composition morphology. The process parameter list includes the following topics: layer thickness, hatch, laser spot diameter and power. Finally, scanning speed needs to be considered. While layer thickness is affected by matters depending on the component target surface finishing degree resolution, the laser spot diameter is usually fixed on commercial 3d printers. The optimized process needs to take into account the determination of the best laser power and speed as well of the hatch distance. Therefore in order of selective laser melting process optimization, tools able to define the operating window in the P-v (laser beam power – velocity) space are needed. Such tools are required to take into account the dependence of such items on metals composition and powder morphology. Several approaches have been developed for the above problem [19-22]. In the approach reported in [23], the process mapping simply gets to the process outcomes of an additive manufactured process, jus considering input power and speed. Usually, constant cross-sectional area curves are plotted to allow to determine the power and speed combinations resulting in a similar melt pool cross-sectional area. Numerical modelling of the track melting has been approached by the use of commercial finite element software’s [24-26]. In particular [27] reports about experiments carried out at the National Institute of Standards and Technology (NIST) on an Inconel 625 plate using an EOSINT M270 Laser Powder Bed machine. A test matrix of several powers and speed values combinations was originated, covering the full standard operating region of the considered 3D printer. Laser process simulations were carried out using a 3D finite element model. Results of the simulation were compared with the experimental cross-sectional areas. A not perfect fitting was obtained using a fixed value of effective laser absorptivity of 0.57, inducing to hypothesize better fitting for an absorptivity varying with laser power and speed. In this paper, we propose a modelling tool able to generate processing maps of alloys suitable to the laser powder bed fusion technique. A simplified physical frame is modelled to reduce computing time. The model is then applied covering process parameters ranges typical of the specific additive manufacturing machine. The output is the limits of the conduction, transition and keyhole modes in the laser power-velocity plane, along with the full dense region. Experimental data concerning different thermo-physical alloys properties are needed to validate the model. Three data sources have been selected throughout the literature at this first step of the model evolution [28-33]. The model The continuous modification of the melt pool as the specific laser energy is due to the gas/melt surface evaporation onset and occurs when the temperature is high enough. The conduction mode ends up and a recoil momentum [10] is produced modifying the initially flat gas/melt interface and leading to an increasingly deeper cavity as the laser entering specific energy is enhanced. As the cavity deepens, higher energy values are absorbed into the cavity due to multiple ray reflections against the cavity interface [29]. Due to this mechanism, a shallow