The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Carolin Körner - One of the best experts on this subject based on the ideXlab platform.

  • predictive simulation of process windows for Powder bed fusion additive manufacturing influence of the Powder bulk density
    Materials, 2017
    Co-Authors: Alexander M. Rausch, Matthias Markl, Vera E. Küng, Christoph Pobel, Carolin Körner
    Abstract:

    The resulting properties of parts fabricated by Powder bed fusion additive manufacturing processes are determined by their porosity, local composition, and microstructure. The objective of this work is to examine the influence of the stochastic Powder bed on the process window for dense parts by means of numerical simulation. The investigations demonstrate the unique capability of simulating macroscopic domains in the range of millimeters with a mesoscopic approach, which resolves the Powder bed and the hydrodynamics of the melt pool. A simulated process window reveals the influence of the stochastic Powder Layer. The numerical results are verified with an experimental process window for selective electron beam-melted Ti-6Al-4V. Furthermore, the influence of the Powder bulk density is investigated numerically. The simulations predict an increase in porosity and surface roughness for samples produced with lower Powder bulk densities. Due to its higher probability for unfavorable Powder arrangements, the process stability is also decreased. This shrinks the actual parameter range in a process window for producing dense parts.

  • a coupled cellular automaton lattice boltzmann model for grain structure simulation during additive manufacturing
    Computational Materials Science, 2016
    Co-Authors: A Rai, Matthias Markl, Carolin Körner
    Abstract:

    Abstract A 2D coupled Cellular Automaton (CA)–Lattice Boltzmann (LB) model has been developed to simulate grain structure evolution during Powder–bed–based, Layer by Layer, additive manufacturing (AM). The presented model includes algorithms for random Powder Layer generation, electron beam energy absorption, evaporation, capillarity and wetting, meltpool dynamics, its temperature evolution and face centered cubic grain solidification. The model is first validated against the experimental findings of single track electron beam melting and solidification of a baseplate and then applied to simulate the grain structure produced during AM. Influence of the hatching strategy on grain structure is presented as well as stray grain formation resulting from partially molten Powder particles.

  • defect generation and propagation mechanism during additive manufacturing by selective beam melting
    Journal of Materials Processing Technology, 2014
    Co-Authors: A Bauereis, T Scharowsky, Carolin Körner
    Abstract:

    Abstract During Powder bed based additive manufacturing processes a component is fabricated by locally melting of Powder Layers with a laser or an electron beam. The fast melting process of the stochastic Powder bed induces vigorous melt pool movements which sometimes lead to faults acting as starting points for larger defects such as channels bridging many Layers. Since the formation of these defects cannot be understood in the framework of a homogenized numerical approach we have developed a mesoscopic numerical model based on the Lattice Boltzmann Method for the local melting process which considers individual Powder particles. The model takes into account full hydrodynamics including capillary and wetting effects. It is shown that these effects combined with the stochastic Powder Layer are the origin of fault formation. The numerical results are compared with experiments in order to demonstrate the predictive value of our model.

I Smurov - One of the best experts on this subject based on the ideXlab platform.

  • model of heat and mass transfer in random packing Layer of Powder particles in selective laser melting
    Physics Procedia, 2014
    Co-Authors: O B Kovalev, I Kovaleva, I Smurov
    Abstract:

    Abstract Discretegrid model of heat transfer in granular porous mediumto describe the processes of selective laser melting of Powdersis developed. The thermal conductivity in this mediumis performed through thecontact surfaces between the particles. The calculation method of morphology of random packing Layer of Powder considering the adhesive interaction between the particles is proposed. The internal structure of the obtained loose Powder Layer is a granular medium where spherical particles of different sizes are arranged in contact with each other randomly. Analytical models of Powder balling process and formation of the remelted track are proposed.

  • energy input effect on morphology and microstructure of selective laser melting single track from metallic Powder
    Journal of Materials Processing Technology, 2013
    Co-Authors: Igor Yadroitsev, Pavel Krakhmalev, Ina Yadroitsava, Sten Johansson, I Smurov
    Abstract:

    Abstract Process parameters of selective laser melting affect the response of a Powder–substrate system and, therefore, the geometry and microstructure of the manufactured parts. The experiments were carried out at fixed values of laser power (50 W), spot diameter (70 μm) and Powder Layer thickness (80 μm). In this research, influence of the energy input parameters (80–900 °C preheating temperature and 0.08–0.28 m/s laser scanning speed) on microstructure and geometry of single tracks fabricated of stainless steel grade 316L Powder was analysed. Both factors were found statistically significant with regard to their influence on the remelted depth and the primary cell spacing in the colonies observed in the tracks cross-sections. More specifically, the contact angle and track height were controlled by the preheating temperature, and track width and contact zone characteristics were governed by the laser scanning speed. Because of the threshold behaviour of these two factors, values starting with 700 °C and 0.24 m/s were found not optimal and causing instability and balling effect. Conclusions regarding the selection of process parameters for the formation of tracks with the desired geometry and microstructure were formulated based on statistical analysis of the experimental data.

  • selective laser melting technology from the single laser melted track stability to 3d parts of complex shape
    Physics Procedia, 2010
    Co-Authors: Igor Yadroitsev, I Smurov
    Abstract:

    To up-grade SLM process for manufacturing real components, high mechanical properties of final product must be achieved. The properties of a part produced by SLM technology depend strongly on the properties of each single track and each single Layer. In this study, effects of the processing parameters such as laser power, scanning speed and Powder Layer thickness on the single tracks formation are analyzed. It is shown that, by choosing an optimal technological window and appropriate strategy of SLM, it is possible to manufacture highly complex parts with mechanical properties comparable to those of wrought material.

  • modeling the interaction of laser radiation with Powder bed at selective laser melting
    Physics Procedia, 2010
    Co-Authors: A V Gusarov, I Smurov
    Abstract:

    Obtaining uniform single vectors well attached to the substrate is necessary and sufficient for fabrication of complex-shape parts of high quality by selective laser melting. The temperature distribution in the laser/Powder interaction zone and the shape of the melt pool is numerically calculated by the proposed model of coupled radiation and heat transfer applicable to single vectors. The analysis of the capillary stability of the segmental cylinder applied to the calculated melt pool estimates the stability of the process depending on the scanning velocity, Powder Layer thickness, and the material optical and thermal properties.

  • heat transfer modelling and stability analysis of selective laser melting
    Applied Surface Science, 2007
    Co-Authors: A V Gusarov, Igor Yadroitsev, Ph Bertrand, I Smurov
    Abstract:

    Abstract The process of direct manufacturing by selective laser melting basically consists of laser beam scanning over a thin Powder Layer deposited on a dense substrate. Complete remelting of the Powder in the scanned zone and its good adhesion to the substrate ensure obtaining functional parts with improved mechanical properties. Experiments with single-line scanning indicate, that an interval of scanning velocities exists where the remelted tracks are uniform. The tracks become broken if the scanning velocity is outside this interval. This is extremely undesirable and referred to as the “balling” effect. A numerical model of coupled radiation and heat transfer is proposed to analyse the observed instability. The “balling” effect at high scanning velocities (above ∼20 cm/s for the present conditions) can be explained by the Plateau–Rayleigh capillary instability of the melt pool. Two factors stabilize the process with decreasing the scanning velocity: reducing the length-to-width ratio of the melt pool and increasing the width of its contact with the substrate.

Yifu Shen - One of the best experts on this subject based on the ideXlab platform.

  • balling phenomena in direct laser sintering of stainless steel Powder metallurgical mechanisms and control methods
    Materials & Design, 2009
    Co-Authors: Yifu Shen
    Abstract:

    Abstract Balling effect, as an unfavorable defect associated with direct metal laser sintering (DMLS), is a complex physical metallurgical process. In this work, two kinds of balling phenomena during DMLS of 316L stainless steel Powder were investigated and the metallurgical mechanisms of balling were elucidated. It was found that using a low laser power gave rise to the first kind of balling characterized by highly coarsened balls possessing an interrupted dendritic structure in the surface Layer of balls. A limited amount of liquid formation and a low undercooling degree of the melt due to a low laser input was responsible for its initiation. The second kind of balling featured by a large amount of micrometer-scaled (∼10 μm) balls on laser sintered surface occurred at a high scan speed. Its formation was ascribed to laser-induced melt splashes caused by a high capillary instability of the melt. Feasible control methods were proposed to alleviate balling phenomena. It showed that increasing the volumetric density of energy input, which was realized by increasing laser power, lowering scan speed, or decreasing Powder Layer thickness, decreased the tendency of balling. The addition of a trace amount of deoxidant (H 3 BO 3 and KBF 4 ) in the Powder yielded a smooth laser sintered surface free of balling.

  • Processing conditions and microstructural features of porous 316L stainless steel components by DMLS
    Applied Surface Science, 2008
    Co-Authors: Yifu Shen
    Abstract:

    Abstract Direct metal laser sintering (DMLS), due to its flexibility in materials and shapes, would be especially interesting to produce complex shaped porous metallic components. In the present work, processing conditions and microstructural characteristics of direct laser sintered porous 316L stainless steel components were studied. It was found that a partial melting mechanism of Powders gave a high feasibility in obtaining porous sintered structures possessing porosities of ∼21–∼55%. Linear energy density (LED), which was defined by the ratio of laser power to scan speed, was used to tailor the laser sintering mechanism. A moderate LED of ∼3400–∼6000 J/m and a lower scan speed less than 0.06 m/s proved to be feasible. With the favorable sintering mechanism prevailed, lowering laser power or increasing scan speed, scan line spacing, and Powder Layer thickness generally led to a higher porosity. Metallurgical mechanisms of pore formation during DMLS were addressed. It showed that the presence of pores was through: (i) the formation of liquid bridges between partially melted particles during laser irradiation; and (ii) the growth of sintering necks during solidification, leaving residual pores between solidified metallic agglomerates.

Panagiotis Michaleris - One of the best experts on this subject based on the ideXlab platform.

  • selection of Powder or wire feedstock material for the laser cladding of inconel 625
    Journal of Materials Processing Technology, 2016
    Co-Authors: Jarred C Heigel, Panagiotis Michaleris, Michael Gouge, T A Palmer
    Abstract:

    Abstract The selection of the feedstock material form significantly affects the temperature and resulting distortion generated during laser cladding. An experimental investigation is undertaken to characterize the differences in temperature and deformation histories resulting from laser cladding using Powder and wire. While both feedstock produce good quality clads, the Powder clad is nearly twice as thick as the wire clad. In situ measurements show that the selection of a Powder feedstock results in higher temperatures and greater deformation. However, characterization of the final distortion shows that each clad twists the substrate by nearly the same amount. Thermo-mechanical modeling of the process shows that the disparity in laser absorption efficiency is responsible for the variation in temperature between the Powder and wire. Simulations of a multi-Layer deposition show that although a single wire Layer generates lower temperatures and less deformation than a single Powder Layer, the wire clad will actually produce greater total deformation because two Layers are required to achieve the same thickness as the Powder clad.

  • Thermal modeling of Inconel 718 processed with Powder bed fusion and experimental validation using in situ measurements
    Additive Manufacturing, 2016
    Co-Authors: Erik R Denlinger, Vijay Jagdale, Tahany El-wardany, G. V. Srinivasan, Panagiotis Michaleris
    Abstract:

    A model for predicting the thermal response of Inconel® 718 during laser Powder-bed fusion processing (LPBF) is developed. The approach includes the pre-placed Powder Layer in the analysis by initially assigning Powder properties to the top Layer of elements before restoring the solid properties as the heat source traverses the Layer. Different linear heat inputs are examined by varying both laser power and scan speed. The effectiveness of the model is demonstrated by comparing the predicted temperatures to in situ experimental thermocouple data gathered during LPBF processing. The simulated temperatures accurately capture the measured peak temperatures (within 11% error) and temperature trends. The effect of neglecting the pre-placed Powder Layer in the simulations is also investigated demonstrating that conduction into the Powder material should be accounted for in LPBF analyses. The simulation neglecting the Powder predicts temperatures more than 30% higher than the simulation including the Powder.

Yuwen Zhang - One of the best experts on this subject based on the ideXlab platform.

  • Analysis of melting in a subcooled two-component metal Powder Layer with constant heat flux
    Applied Thermal Engineering, 2006
    Co-Authors: Tiebing Chen, Yuwen Zhang
    Abstract:

    Abstract Melting of a subcooled two-component metal Powder Layer is investigated analytically. The Powder bed considered consists of a mixture of two metal Powders with significantly different melting points. Shrinkage induced by melting is taken into account in the physical model. The temperature distributions in the liquid and solid phases are obtained using an exact solution and an integral approximate solution, respectively. The effects of porosity, Stefan number, and subcooling on the surface temperature and solid–liquid interface are also investigated. The present work provides a strong foundation upon which the investigation of complex three-dimensional selective laser sintering (SLS) process can be based.

  • numerical simulation of two dimensional melting and resolidification of a two component metal Powder Layer in selective laser sintering process
    Numerical Heat Transfer Part A-applications, 2004
    Co-Authors: Tiebing Chen, Yuwen Zhang
    Abstract:

    Selective laser sintering (SLS) of metal Powder is an emerging technology by which metal parts can be fabricated in a Layer by Layer fashion. SLS of the first Layer is modeled as melting and resolidification of a metal Powder Layer subject to a moving heat source on top, while the bottom is adiabatic. SLS of the consecutive Layer is modeled as melting and resolidification of a metal Powder Layer on top of the existing multiple resolidified Layers. The results indicate that the thicknesses of the loose metal Powder Layer, the moving heat source intensity, and the scanning velocity have significant effects on the sintering process in both the first Layer and each subsequent Layer. A parametric study is performed, and the best combination of processing parameters is recommended.

  • Melting and Resolidification of a Two-Component Metal Powder Layer Heated by a Moving Gaussian Heat Source
    Heat Transfer Volume 3, 2003
    Co-Authors: Tiebing Chen, Yuwen Zhang
    Abstract:

    Melting and resolidification of a subcooled mixed metal Powder Layer that contains a mixture of two metal Powders with significantly different melting points heated by a moving Gaussian heat source is investigated numerically. The phase change is modeled using a temperature-transforming model and shrinkage induced by melting is also taken into account. The problem appears to be steady-state since it is formulated in a coordinate system moving with the Gaussian heat source and the size of the Powder is much larger than that of the heat source. The results show that the Powder Layer thickness, moving heat source intensity and scanning velocity have significant effects on the sintering depth.Copyright © 2003 by ASME