Evaluation methodology for 3D printing allows greater design variety

October 22, 2018 // By Christoph Hammerschmidt
Evaluation methodology for 3D printing allows greater design variety
Additive manufacturing, aka 3D printing, has established itself as a flexible manufacturing method in the production of metallic structures. In addition to the possibility of producing components in shapes that are not possible with conventional processes, 3D printing offers a direct link between the production process and the digital model. For the production of cyclically loaded components, however, the process cannot yet be used properly, because design standards are not yet available. The Fraunhofer Institute for Structural Durability and System Reliability LBF wants to change this and is dedicating several research projects to this topic.

In the additive manufacture of components using selective laser melting, the parameters of the process have an effect on the material produced. This can affect, for example, the production of the powder or the exposure strategy when melting the powder. The Fraunhofer LBF is currently working on questions concerning the effects and influence of cyclic material behavior by parameters of selective laser melting as well as their consideration within the framework of a numerical stress analysis for estimating the service life of cyclically stressed components.

First test results on specimens with polished surfaces left in the production state provided the scientists with information about the complex effects of selective laser melting on the material and component properties. As expected, the surface quality has a decisive influence on the service life. The rough, additive surface represents a potential failure location under cyclic loading, especially if process-related support structures are required for the production of overhanging component geometries. In addition to the component surface, internal irregularities such as pores are not only relevant for failure in the core material, but increasingly in the edge area of additively manufactured structures.

The test results of the Fraunhofer LBF underline that the stress level and the construction direction have an effect on the cyclic yield strength of the additive aluminium alloy AlSi10Mg. This property is direction-dependent, but can be compensated by a guided heat treatment.

Based on the experimental findings, the Fraunhofer LBF took the first conceptual steps to optimize a design concept for cyclically stressed components and structures in order to evaluate and accurately describe their specific material properties. The scientists take into account important influencing variables such as internal irregularities, surface properties, the anisotropy of the microstructure or residual stress states, which affect the mechanical and geometric properties. In doing so, they start from existing design methods for metallic components, which are used in the classical manufacturing processes of casting and welding, and

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