# Fabrication of Mesh Patterns Using a Selective Laser-Melting Process
## 4 Selective Laser Melting (SLM) of Thin Mesh Patterns  
Figure 10 shows the three mesh types fabricated in this study. Mesh patterns with dimensions of \(20\times 20\times 0.4\) mm were built using the SLM process on a copper plate. The line spacing of the meshes was 0.82, 0.82, and 2 mm for square, circular, and rectangular shapes, respectively. The layer was made of AISI 304 stainless steel powder on a copper plate. To see the effect of copper plate, the molten-pool temperatures for AISI 304 stainless steel and copper base plates are compared by FE simulations. Figure 11 shows the molten-pool temperatures obtained for the two different base plates. As the thermal conductivities of the base plates differed, the geometries and temperatures of the molten pools also changed. When using the AISI 304 stainless-steel base plate, the temperature of the plate surface is above the liquidus temperature, and the molten pool is expected to adhere to the base plate, due to local fusion. In the case of the copper base plate, the rapid heat dissipation due to the enhanced thermal conduction can reduce the possibility of local adhesion. However, the overall molten-pool area obtained for the AISI 304 stainless-steel base plate is larger than that of the copper base plate, due to the reduced heat dissipation. Figure 10: Computer-aided design (CAD) models of different mesh types: (**a**) square, (**b**) circular, and (**c**) rectangular holes. Figure 9: Von-Mises stress for two different scan tracks; (**a**) straight track, (**b**) circular track. For the validation purpose, the multi-track bead shapes obtained from experiments for the two different base plates are shown in Figure 12. When using the AISI 304 stainless-steel base plate, the molten pool adheres to the base plate due to the local fusion. In the case of the copper base plate, no adhesions are observed along the boundary due to the rapid heat dissipation due to the enhanced thermal conduction. The overall layer height obtained for the AISI 304 stainless-steel base plate is 100-150 \(\upmu\)m larger than that of the copper base plate, due to the reduced heat dissipation. Figure 13 shows a schematic drawing of the mesh fabrication method applied. As shown in the figure, powder is layered on the copper plate at a layering thickness of 0.5 mm. Then, the laser beam is irradiated according to the CAD data of the mesh shape. As obtained by the FE simulations described in Section 3, straight scan track has been applied in the SLM process. After completing the irradiation, the fabricated mesh part is detached from the copper plate. Figure 11: Comparison of molten pool temperatures for different base plates: (**a**) AISI 304 stainless steel and (**b**) copper base plate. Figure 12: Comparison of multi-track bead shapes for different base plates: (**a**) AISI 304 stainless steel and (**b**) copper base plate. Figure 13: Schematic drawing of mesh part fabrication. Figure 14 shows images of SLM-fabricated mesh parts having square, circular and rectangular holes with a size of \(20\times 20\) mm. As the figure shows, sound mesh parts with the target dimensions are quickly obtained through a single continuous irradiation. Figure 15 shows an optical microscope image of the mesh part obtained. The bead has a continuous and dense appearance. According to the optical microscope image obtained at 500\(\times\) magnification, the microstructure consists of a \(\gamma\)-austenite matrix with \(\delta\)-ferrite having a dendrite size of about 20 \(\upmu\)m. During the solidification of austenitic stainless steel, such as AISI 304 stainless steel, the first phase to solidify as the temperature drops below the point of peritectic transformation is \(\delta\)-ferrite [46]. Hence, \(\delta\)-ferrite tends to transform into austenite (\(\gamma\)) during cooling. The phase transformation from \(\delta\)-ferrite into \(\gamma\)-austenite depends on the diffusion mechanism through a solid phase.