Different path strategies for directed energy deposition of crossing intersections from stainless steel SS316L-Si

Additive manufacturing by directed energy deposition is of increasing interest within the scientific community. Over the past decade, this technology has gained ground with the production of parts from SS 316L-Si stainless steel, an industrial product in widespread use. Yet one of the main challenges when extending the use of this technology to the manufacture of medium complexity parts is how to achieve good intersections. This paper focuses on the use of Plasma Arc Welding (PAW) for the additive manufacturing of X-Cross intersections made of SS 316L-Si stainless steel alloy, defining its geometrical suitability and evaluating its productivity. Firstly, two strategies for the production of parts are presented: the energy control strategy on the curved path of a L-shaped wall and the variable amplitude waveform strategy (variable waving) for the continuous production of a X-cross intersection. A metallographic analysis of the samples extracted in the different tests was completed, focusing mainly on the transversal direction. Next, four deposition strategies based on discrete trajectories (cross-overlapping and cross-waving) and on continuous trajectories (waving and overlapping) are addressed in this paper for the production of cross intersections in a part of medium complexity and for the extension of its use in Near-Net-Shape (NNS) manufacturing. The mechanical properties and microstructure of samples manufactured with these deposition strategies are analysed by means of tensile tests and metallographic characterization. An analysis of the deposition energy and of the productivity is carried out for the four strategies. The productivity is analysed by means of different parameters such as the number of layers, the actual deposition rate and process times (deposition time, waiting time, standby time and idle time). The most advantageous strategies in terms of productivity were cross-waving and waving, achieving torch utilization rates relative to total time of 50 %. Methodologies and conditions for the manufacture of X-cross intersections are established. Finally, a study of the cross-intersection geometry obtained for each deposition strategy is performed. From the geometrical analysis of the crosses produced, it has been observed that the ratio of material used in the cross-overlapping sequence to produce a X-cross intersection in relation to the amount of material deposited is more than 10 % higher than in the other strategies.