Page 53 - MSAM-1-3

Materials Science in Additive Manufacturing Characterization of TPMS structures

using laser PBF (LPBF) to manufacture such structures experimentally tested values and the values predicated
on an industrial scale. The first is the limitations of the by the Gibson-Ashby model. Many other scholars
stereolithography (STL) file format. It is difficult and have investigated the microstructure and mechanical
time-consuming for commercial pre-processing software deformation behavior of LPBF-produced lattice structures.
(i.e., Magics, Voxel Dance, and P3Ds) to handle the STL However, to the best of our knowledge, all of these studies
model of lattice/cellular structures created by scholars used the conventional AM data-processing method when
using the proposed novel design methods when the printing the lattice structure. As pointed out by Neikter
[19]
number of structural units exceeds ten thousand or more. et al. , the microstructure of LPBF-produced samples is
Second, it is difficult to evaluate the manufacturability and related to the laser scanning strategy, that is, the toolpath.
manufacturing results of such complex structures because However, the toolpath generated by the toolpath-based
traditional evaluation methods are unsuitable for AM construction method is different from that generated by
processes . Finally, the performance (i.e., physical and commercial AM data pre-processing software. Hence, it is
[8]
mechanical properties, and failure mechanism) of such unknown whether the performance of a lattice structure
novel structures is still unclear, although many scholars fabricated using toolpath-based construction design is the
have focused on this topic. same as that of the traditionally designed structures.
To solve the first problem, Ding et al. proposed an In summary, there is a gap in knowledge regarding the
[12]
STL-free design and manufacturing paradigm for high- microstructure and mechanical performance of lattice
precision PBF, and Feng et al. [13,14] proposed an efficient structures obtained using toolpath-based design. To fill this
generation strategy for hierarchical porous scaffolds with gap, we fabricated a TPMS Schwarz-P structure using our
freeform external geometries. Both groups simplified the proposed method and investigated its microstructure and
three-dimensional (3D) calculations to two-dimensional mechanical performance. The rest of the paper is organized
(2D) operations to improve the calculation efficiency. as follows: Section 2 introduces the experimental materials
However, the infilling efficiency remains a problem. and methods, Section 3 gives the experimental results and
Similar to this simplified method, we proposed a toolpath- discusses the results, and we conclude with Section 4.
based construction method for designing and printing 2. Materials and methods
porous structures in a previous study . In our method,
[15]
we used a toolpath pattern to infill the hull model, directly 2.1. TPMS Schwarz-P surface
generating the toolpath of the porous structure. Compared [3]
with the traditional pre-processing method, the toolpath- A TPMS is an implicit surface with zero mean curvature .
based construction method exhibits a significant advantage Owing to their smooth surfaces and highly interconnected
in terms of toolpath precision and generating efficiency. porous architectures, TPMS structures have been applied
in many domains. The Schwarz-P surface is a typical type
However, as mentioned above, to apply cellular of TPMS. Equation I gives its mathematical expression,
structures generated by toolpath-based construction on and Figure 1 shows Schwarz-P surfaces with different unit
an industrial scale, the manufacturability/manufacturing sizes and shape factors.
results and structural performance still need to be
investigated. Although we analyzed the manufacturability xy z,, :cos 2 x cos 2 y cos 2 zc (I)

of a cellular structure generated using the toolpath-based k k k
construction method and developed a manufacturability
predictor for these structures in previous papers [15,16] , we 2.2. Toolpath-based construction method
did not investigate the performance of structures generated In this study, a toolpath-based construction method
by the toolpath-based method.
was used to construct and generate printing toolpaths
Yan et al. evaluated the manufacturability and for the TPMS-Schwarz-P structures. Figure 2 shows
[17]
performance of LPBF-produced TPMS gyroid lattice the workflow of the printing toolpath generation of the
structures. They found that the yield strength and Young’s TPMS-Schwarz-P structure through the toolpath-based
modulus of the gyroid lattice structures increased with construction method. The hull model, AM parameters,
decreasing unit cell size because of the denser struts of the and mathematical equation of the Schwarz-P surface and
lattice structures with smaller unit cell sizes. In another its corresponding toolpath pattern were used as the input
study, Yan et al. established two equations based on variables in this method. As shown in Figure 2, the box
[18]
the Gibson-Ashby model to predict the compression model was first sliced at a fixed thickness to obtain the
properties of the 316L stainless steel gyroid lattice layer contours. Then, the layer contours were used to
structures; however, there were differences between the construct the polygons to be infilled. Finally, the polygons

Volume 1 Issue 3 (2022) 2 http://doi.org/10.18063/msam.v1i3.17