Dimensional assessment of uniformly periodic porosity primitive TPMS lattices using additive manufacturing laser powder bed fusion technique

Triply periodic minimal surface (TPMS) lattices have been heavily investigated lately due to their superior thermo-mechanical performance compared with their lattice counterparts. The advancement of additive manufacturing, i.e., laser powder bed fusion (LPBF), has easily enabled the manufacturing of such complex lattices. Recent studies have investigated the heat transfer performance of multiple TPMS lattice types such as gyroid, diamond, IWP, and primitive structures. The primitive TPMS (PTPMS) showed enhanced heat transfer performance mainly due to its cell shape and thickness (i.e., lattice topology). Hence, the lattice dimensional trends and CAD to manufactured dimensional deviation in the overall heat transfer analysis are significant. However, dimensional assessment analysis of PTPMS lattices by LPBF has not been investigated yet. In order to bridge this gap, this study aims at analyzing 17-4 PH stainless steel printed PTPMS lattices at varying cell sizes and porosity. Parameters such as lattice wall thickness, surface area to volume ratio (SA:Vol), pore size, and porosity are investigated. Moreover, the lattice minimum wall thickness and pore size that can reliably be produced are investigated as well. The ORLAS Coherent 250-W LPBF printer was utilized, and its optimized 17-4 PH SS printing parameters were used. Moreover, the machine printing parameters were fixed for all lattice samples; hence, lattice CAD to manufactured dimensional deviation is only dependent on the lattice geometry. Micro X-ray computed tomography (mu CT), which is a non-destructive and accurate method, was used to conduct the analysis. Increasing the PTPMS lattice cell size from 2.9 to 10 mm showed an increase in the lattice wall thickness and pore size but a decrease in the SA:Vol ratio. However, increasing the lattice porosity from 45 to 90% resulted in a decrease in the lattice wall thickness but an increase in both the SA:Vol ratio and pore size. Comparing CAD to manufactured PTPMS lattices, the resulting lattice samples showed lower wall thicknesses and higher SA:Vol ratios than designed which is attributed to shrinkage during the building process. Moreover, the printed lattice pore size and porosity values were observed to be higher than the CAD values. Finally, the minimum PTPMS lattice wall thickness and pore size that can successfully be printed were found to be 152 mu m and 317 mu m, respectively.

Automated summary

This study analyzes the performance of 17-4 PH stainless steel printed PTPMS lattices using LPBF. The results show that increasing the lattice cell size leads to thicker lattice walls and larger pore size, but decreases the SA:Vol ratio. On the other hand, increasing the lattice porosity decreases the lattice wall thickness, but increases both the SA:Vol ratio and pore size. The printed lattice samples exhibit lower wall thicknesses and higher SA:Vol ratios compared to the designed values, which can be attributed to shrinkage during the printing process. The minimum printable wall thickness and pore size for PTPMS lattices are found to be 152 μm and 317 μm, respectively.