Annual report 2018

Additive manufacturing of metallic materials: The path to applicability in safety-critical components.

Additive manufacturing of metallic materials, process characteristics, fatigue life approaches, metallography

Every new manufacturing technology comes along with new challenges. The same applies to additive manufacturing (AM) of metallic materials, which can be used to produce components designed to meet the flux of forces and, hence, for lightweight design. AM-manufactured components must meet high standards in terms of static and cyclic strength, especially in safety-critical applications. Experts at Fraunhofer LBF are exploring the fundamental understanding of the structural behavior of the components and a reliable fatigue design concept for lifetime estimation.

Among other things, the fatigue life of additively manufactured structures is affected by the microstructure, including various defects and in particular the surface. Each of the effects is dependent on the different process parameters. The goal is to understand and assess these effects, so that they can be used in future applications.

In the joint project ”VariKa”, Fraunhofer LBF is responsible for fatigue assessment of the additively manufactured components, which are used in a scalable battery carrier for use in electric vehicles. The entire development process chain in this project, starting from the conceptual design of the battery carrier and updatable production technology with assembly-free joining to the fatigue assessment, is taken into account and optimized to meet the requirements of additive manufacturing. The aluminum material AlSi10Mg is used for this project.

In another joint project, BadgeB, cyclically loaded components made of the nickel-based superalloy Inconel^® 718 and the aluminum-magnesium-scandium alloy Scalmalloy^® are characterized. Both materials are investigated with regard to powder production, additive manufacturing, and application in the aerospace and automotive industries.

In addition to broad experimental and numerical fatigue investigations at Fraunhofer LBF, further analyses of the setup and fatigue failure of AM structures are required in order to develop reliable fatigue design concepts and thus to gain an essential understanding of the cyclic structural behavior and the contributing factors on the service life. Current efforts in the projects focus on the metallographic and fractographic analyses of AM structures produced by selective laser melting, also known as Laser Powder Bed Fusion (LPBF). The variations between target and actual geometry and the different microstructures due to varied process parameters are recorded and their effects on fatigue strength are correlated.