PSI - Issue 8

P. Conti et al. / Procedia Structural Integrity 8 (2018) 410–421

415

Author name / Structural Integrity Procedia 00 (2017) 000–000

Two adjacent scanning paths can overlap and will have opposite scanning vectors. During this process, every cell will be heated up and cooled down many times as the laser beam impinges its neighborhood. While the layers pile up a new scanning pattern (orthogonal to the former) will be added and again every pixel will be heated up to melting temperature and cooled down.

Fig. 6. “Island Scan Strategy” - Gibson et al. (2010)

Fig. 7. Physical description of the model

To consider this scenario, the “birth and death” technique implemented in the commercial code ANSYS was adopted. With this technique, a complete FE model can be built with some elements “active” and some “idle”. At each recursive analysis, the idle elements can be switched on (birth) and active elements can be switched off (death). A control loop determines when an element is activated according to whether its temperature after a load step has surpassed or not the melting point. This a very powerful approach that allows to model the entire structures but each step takes into account only a part of the model. In the present work, the entire stack of layers was modeled at the beginning but only the elements belonging to the scanned layer and the underlying layers where active; this reduces significantly the calculus burden.

Fig. 8. FE model

During the production of a component with SLM, the first layer is attached to e support plate and the layers pile up during the growth. The FE model considers the plate, three layers of powder (at the beginning only the first one will be active and, progressively the other will be switched on thanks to the “birth and death” technology. Fig.7 shows the model, the gray region corresponds to the plate and the brownish region represents the powder. As one can see, a large region around the scanned island is modeled to better simulate the thermal behavior. The FE model was realized with 8-nodes hexahedral elements (SOLID5), every powder layer was split into three elements trough the thickness while the plate is modeled with one element only through the thickness. Fig. 8 displays the meshed model (only one layer is displayed) and the physical dimensions are listed in tab I.