Selective laser sintering (SLS) of powders is an additive manufacturing technique, which allows the construction of three-dimensional objects by adding powder and sintering it layer by layer. The granular material used in this process must have well-defined characteristics, in particular, must be capable of forming a thin and homogeneous layer of about 100 microns. Many factors can affect the flow properties of a powder such as, for example, the particle size, the particle shape, the forces between the particles, the humidity and the temperature [1], which directly or indirectly define the flow properties of the powder used to form the layers. The quality of the powder layer spread in each cycle depends on the procedure followed. Furthermore, often, the techniques adopted to measure the powder flowability involve measuring conditions which are very different from those occurring during the layer formation in SLS [2-3]. This paper proposes a characterization technique of powder quality for SLS application by using a set up that mimics the movements in an SLS apparatus. A roller is used to spread the powder in layer. It works by advancing against a pile of the powder. The set up allows to independently control and the advancement and rotation speed of the roller. The quality of the powder layer produced is characterized by means of an indentation tes carried out with a dynamometer. In particular, the dynamometer allows to assess the degree of compaction of the layer, measuring the force required to penetrate the layer. Subsequently, the tests of mechanical strength carried out on the sintered specimen are used to correlate the characteristics of the powder bed to the final product properties. The paper reports the results of the experiments in which the assessed variables are the translational and the rotational speed of the speed of the roller, the distance between the roller and the previous layer, the amount of solids used to prepare the new layer.

Flowability of powders in the laser sintering process

D. Sofia;D. Barletta;M. Poletto
2018-01-01

Abstract

Selective laser sintering (SLS) of powders is an additive manufacturing technique, which allows the construction of three-dimensional objects by adding powder and sintering it layer by layer. The granular material used in this process must have well-defined characteristics, in particular, must be capable of forming a thin and homogeneous layer of about 100 microns. Many factors can affect the flow properties of a powder such as, for example, the particle size, the particle shape, the forces between the particles, the humidity and the temperature [1], which directly or indirectly define the flow properties of the powder used to form the layers. The quality of the powder layer spread in each cycle depends on the procedure followed. Furthermore, often, the techniques adopted to measure the powder flowability involve measuring conditions which are very different from those occurring during the layer formation in SLS [2-3]. This paper proposes a characterization technique of powder quality for SLS application by using a set up that mimics the movements in an SLS apparatus. A roller is used to spread the powder in layer. It works by advancing against a pile of the powder. The set up allows to independently control and the advancement and rotation speed of the roller. The quality of the powder layer produced is characterized by means of an indentation tes carried out with a dynamometer. In particular, the dynamometer allows to assess the degree of compaction of the layer, measuring the force required to penetrate the layer. Subsequently, the tests of mechanical strength carried out on the sintered specimen are used to correlate the characteristics of the powder bed to the final product properties. The paper reports the results of the experiments in which the assessed variables are the translational and the rotational speed of the speed of the roller, the distance between the roller and the previous layer, the amount of solids used to prepare the new layer.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11386/4716031
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