Deposition strategies for generating cuboid volumes using extreme high-speed directed energy deposition

Abstract

Extreme high-speed directed energy deposition (EHLA) is a variant of directed energy deposition (DED-LB) developed at Fraunhofer ILT in cooperation with RWTH Aachen University. Because of a powder gas jet setup that is aimed at melting particles in the laser beam before they enter the melting pool, high process speeds of up to several hundred meters per minute and a layer thickness as thin as 25  μm can be achieved. EHLA is generally applied for rotationally symmetric coating applications. In previous experiments on a prototype machine of ponticon GmbH, EHLA was used for building up dense volumes, thus qualifying its use for additive manufacturing, now termed EHLA 3D. In this work, using iron-base alloy 1.4404 and a process speed of 40 m/min, cubic volumes are produced with EHLA 3D. Different deposition strategies commonly used in DED-LB are tested for their transferability to EHLA 3D. The results of different deposition strategies achieving the best near net shape geometry are shown in comparison to DED-LB. Furthermore, the influence of the deposition strategy and used technology on thermal management and microstructure are investigated. The best near net shape is achieved in this comparison using a contour-hatch strategy with 1.5 contours per layer and a 90° rotation of the hatch, both for EHLA and DED-LB. The microstructure of EHLA 3D built cubes is more similar to a typical laser powder bed fusion microstructure than to a typical DED-LB microstructure with respect to grain size and structure.