Cassiopée Galy, Research Engineer Additive Manufacturing at IRT Saint Exupéry won 2020 PhD Thesis Award from 3AF, the French scientific society of aeronautic and Space. Her thesis was supervised by I2M Laboratory and SPI Doctorale School of Bordeaux. 

THESIS SUBJECT

Study of the material / process interaction in order to optimize the operating conditions of the SLM additive manufacturing process applied to aluminum alloys

About her thesis

Interest in selective laser melting (SLM) has been growing in recent years, particularly with regard to the production of metal parts. The low density of aluminum alloys, combined with the possible design optimization enabled by additive manufacturing processes,ensures a significant decrease in the mass of structures which is very interesting for manufacturers in the automotive and aerospaceindustries. However, it is difficult to control the final properties of aluminum parts manufactured by SLM because many defects, suchas porosity, hot cracking, and surface roughness, are generated during the process. To better understand how to optimize theperformance of SLM aluminium parts, several studies were conducted during this work: An identification and selection of characterization methods well-adapted to the specificities of metallic materials developedby powder bed additive manufacturing processes was established.

For instance, the comparison of different methods of determining the relative density of parts showed the advantages and disadvantages of each of the techniques; A study of the SLM machine highlighted the influence of various factors (gas flow, positions of specimens on the constructionplate, or methods of depositing the powder) on the final properties of the produced parts. These elements have an impacton the density of the parts, their surface properties, and their mechanical properties. We found that the positioning of a pieceon the tray is a critical step in the preparation of a build that is not to be neglected; Parametric studies carried out on two types of aluminum alloys—AlSi7Mg0,6 and AM205—have shown that the chemicalcomposition of the aluminum alloy used has a significant influence on the set of operating parameters required tomanufacture an acceptable aluminum alloy part. The energy density, ψ, which is the ratio of the laser power to the productof the lasing speed, the hatching distance, and the layer thickness, is conventionally used for the optimization of the operatingconditions in SLM. Our experimental studies performed at different scales (1D and 3D) have shown the limits of this criterion.

The combination of these results with the numerical simulation of the lasing of a single powder bead served as a basis forthe definition of an initial model, the final objective of which will be to optimize the choice of manufacturing parameters.

About 3AF

The activity of 3AF is largely linked to the industrial and research activities, and consequently to the industries and laboratories working for aeronautics and space. Moreover, 3AF maintains constant and privileged relations with the major government departments and agencies as well as with the academic world.As a learned society, 3AF contributes to the generation and dissemination of new ideas in parallel with industry and government authorities.
Finally, through its means of expression and communication, the 3AF allows its members, students, pilots, technicians, engineers and researchers to make their productions or aspirations known through annual competitions.

 PUBLICATION

Cassiopée Galy, Main defects observed in aluminum alloy parts produced by SLM: From causes to conséquences Additive Manufacturing, Volume 22, August 2018, Pages 165-175