Development of a high-speed laser material deposition process for additive manufacturing

Extreme high-speed laser material deposition (EHLA) is a variant of laser material deposition (LMD) with a modified powder gas jet focus. EHLA allows deposition at high process speeds in the range of several hundred meters per minute and the deposition of layers as thin as 25 μm. Feed rates can be in the range of 50 g/min or above. The processing of material combinations with poor weldability or different melting points is possible, with simultaneously smaller heat-affected zone and dilution zone compared to conventional LMD. Until now, EHLA has mainly been used for applying wear-resistant and corrosion-resistant coatings to rotationally symmetric parts, where high process speeds are achieved by rotation of the substrate. Developing EHLA for additive manufacturing (AM) aims at manufacturing highly individualized parts with high volume buildup rates and finer structural resolution compared to conventional LMD. The main steps toward harnessing EHLA for AM, termed EHLA 3D, are (a) process parameter development for volume buildup through deposition of multiple layers on top of each other and (b) the development of system technology that allows relative spatial movement between the powder nozzle and the substrate at high speeds and high accuracy in three dimensions. With a fast back-and-forth motion, high acceleration rates are necessary to ensure high volume buildup rates and high powder deposition efficiency. In this work, a specially designed tripod machine concept that has been developed in cooperation at Fraunhofer ILT is introduced. Theoretical considerations concerning achievable powder deposition efficiency as a function of process speed and acceleration of the handling system are presented. Furthermore, the results of process parameter development for up to 40 m/min with the iron-base alloy 1.4404 are shown. Virtually pore-free deposition of cuboid volumes is demonstrated. The mechanical values of the additively manufactured volumes are compared to the values for solution-annealed material, conventional LMD-manufactured samples, and samples produced by laser powder bed fusion (LPBF). Finally, an outlook on future research activities required for further development of EHLA 3D is given, covering system technology, buildup strategies, software integration, and possible applications of the new technology in repair, coating, and (hybrid-)additive contexts.