This work explores the use of thermo-structural finite element models (FEM) not just as a predictive diagnostic tool for metal additive manufacturing (MAM), but as an exploratory tool to conduct parametric studies and explore time-variant parameters.
First, a thermo-structural model of Directed Laser Deposition (DLD) is created using ANSYS Parametric Design Language (APDL). The DLD model was first calibrated using a simple experimental setup then validated using two sets of experimental data reported in the literature: A single-layer cladding process and a thin wall build. Once validated, the thermal component of the model was modified to also apply to powder bed fusion (PBF) processes. This involved developing a methodology to estimate the complex scan patterns and high scan speeds inherent to the PBF process that make it challenging to model. PBF results were then experimentally validated using two geometries: A 25-cylinder array, and a square plate.
Finally, this work explored the utility of time-variant parameters, i.e., AM process parameters that are varied at certain intervals instead of remaining constant throughout the process. This was done by incorporating the thermo-structural DLD model into a hill-climbing optimization algorithm. It is found that time-variant laser power can reduce variations in molten pool temperature in the cladding process, leading to reduced cooling rates which are expected to improve structural outcomes. A comparison is drawn with real-time closed feedback AM.
The algorithm was then used to explore the use of time-variant laser power on the thin wall build, and was found to substantially improve both thermal and structural performance. The algorithm also demonstrated the value of conducting thorough investigations of the design space using formal optimization techniques when conducting parametric studies; by studying the effect of dwell time on substrate deflection in the thin wall, it was shown that trends do not hold for a range of dwell times.
To sum up, this work offers evidence for the following novel ideas: