TWI produced double cantilever parts (as shown in Figure 1) using a Renishaw AM250 machine. All parts were produced using Ti-6Al-4V Grade 23 metal powder with a powder particle size range between 15 and 45μm. A 90° alternating scan strategy was used, comprising a series of parallel hatch lines and four boundary contours, rotated by 90° every layer.
After manufacturing the double cantilevers, TWI used wire electrical discharge machining to cut the support structures just below the solid beam surfaces. Upon cutting, the presence of residual stresses generated deflections of the remaining double-sided cantilever beam structure. The out-of-plane deflections were measured using a FaroArm precision measuring tool.
The simulations used new physics-based FEM formulations available in Abaqus 2017 from the SIMULIA brand of Dassault Systèmes. The new features of Abaqus 2017 enable the exact machine information about the powder recoating sequence, laser scan path, and process parameters to be directly input in the FE model. These state-of-the-art capabilities enable progressive element activation, progressive heating computations and cooling of the evolving solid surface of the part as the build progresses.
The simulation model employed temperature-dependent material properties for the heat transfer and stress analysis simulations. An image of the residual stresses after the wire cutting is shown in Figure 2.
The measured deflections from the test pieces were compared with the FEM predictions as shown in Figure 3. There is strong agreement between the predictions and measurements, leading to confidence in the use of this new modelling approach.