The downside of downskin: an overhang ratio to digitally evaluate printability of complex architectures by laser powder bed fusion additive manufacturing

Abstract

Additive manufacturing (AM) enables new possibilities for the design and manufacturing of complex metal architectures. Incorporating lattice structures into complex part geometries can enhance strength-to-weight and surface area-to-volume ratios for valuable components, particularly in industries such as medicine and aerospace. However, when it comes to metal AM technologies like laser powder bed fusion (LPBF), the design parameters of lattice structures and their interconnections may result in unsupported downskin surfaces, potentially limiting their manufacturability. This study aimed to examine the correlation between downskin surface area and the manufacturability of lattice structures fabricated using LPBF. Image processing algorithms were used to analyze the downskin surface areas of seven unique lattice designs and to devise quantitative metrics (such as downskin surface area, discrete surface count, surface inter-connectivity, overhang ratio, overprint/underprint volumes, etc.) to evaluate LPBF manufacturability. The seven lattice designs were subsequently manufactured using maraging steel via LPBF, and then examined using imaging using X-ray micro-computed tomography (XCT). The geometric accuracy of the lattice designs was compared with XCT scans of the manufactured lattices by employing a voxel-based image comparison technique. The results indicated a strong relationship between downskin surface area, surface interconnectivity, and the manufacturability of a given lattice design. The digital manufacturability evaluation workflow was also applied to a medical device design as an example, further affirming its potential industrial utility for complex geometries.