PSI - Issue 13

Richard J. Williams et al. / Procedia Structural Integrity 13 (2018) 1353–1358 Richard J. Williams et al./ Structural Integrity Procedia 00 (2018) 000–000

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Recently, significant research has focused on part scale modelling the LPBF process, however it has frequently relied upon implementing a bespoke code and long solution times are common (Hodge et al. (2014)). Many authors have focused on representing as much of the process physics as possible. Conversely, the ‘inherent strain’ methodology has been employed with the goal of reducing solution time, however this is not without its drawbacks (Bugatti and Semeraro (2018)). Many of the validation scenarios reported in the literature have also focused exclusively on qualifying the accuracy of the model and have not offered as much insight into the stress state of the component considered. In this work, following the approached detailed in Williams et. al. (2018), a finite element model has been developed of the LPBF process, in order to study the influence of build orientation on component stress state and net shape. Solid cylindrical components have been manufactured in both the vertical and horizontal orientation, with respect to the build direction. The cylinders were then slit by wire EDM, part relaxing residual stresses, and the distorted profile was measured to validate the FE predictions. The FE predictions of the component stress fields are then examined to assess the influence of build orientation on the part net shape. 2. Experimental validation Two solid cylindrical components of diameter 8 mm and length 60 mm were built, one denoted horizontal with its axis perpendicular to the build direction and the other denoted vertical with its axis parallel to the build direction, as illustrated in Fig. 1. The parts were built on a Renishaw AM250 using 316L stainless steel (316L) with manufacturer recommended parameters, detailed in Davies et al. (2018). After sectioning from the build plate, the cylinders were slit through the diameter to a depth of 50 mm by wire EDM of thickness 0.25 mm. A schematic of the components and detailing the slitting operation can be seen in Fig. 1.

Build direction

Fig. 1. Schematic detailing the (a) horizontal; (b) vertical build and slitting scenario

During removal from the build plate the horizontal component curled up slightly, whereas the vertical component did not. Post slitting procedure, the residual stress relief caused the vertical component to splay apart whilst the horizontal did not appear to deflect, as illustrated in Fig 2.

(c)

(a)

EDM slit

(b)

Support Structures

Fig. 2. Photographs showing the (a) horizontal top view; (b) horizontal side view (c) vertical side view cylinders after sectioning from build plate and slitting