Computation of spatial intensity distributions for laser powder bed fusion through the solution of an inverse heat conduction problem

In Laser Powder Bed Fusion (LPBF), process productivity, stability and quality depend largely on the intensity distribution used. While current state of the art manufacturing machines use Gaussian or ring-shaped intensity profiles, the latest developments in beam shaping optical components allow for spatial and temporal intensity distributions with a much larger number of degrees of freedom. Nevertheless, the large parameter space associated with this makes it difficult to determine advantageous intensity distributions through experimental investigations or classic process simulations. In this work, a reduced process model is presented that enables the determination of such intensity distributions by solving the inverse heat conduction problem for LPBF based on the conjugate gradient method with an adjoint problem. For this purpose, an FEM-based heat conduction simulation is used that models the temperature distribution of an LPBF process by taking temperature-dependent material parameters into account. In particular, the powder bed is modeled by applying effective thermal properties and an adapted volumetric heat source that models the scattering within the powder bed. This allows for investigating the influence of process-sided asymmetries in the material properties as they occur for example during multi-track experiments. It is shown that these asymmetries have an influence on the optimized intensity distribution and should be considered for the integration of optical systems when using LPBF machines with the newest beam shaping technologies.