# Fabrication of Mesh Patterns Using a Selective Laser-Melting Process
## 2 Material and Process Characterization  
Figure 2 shows the morphology of spherical AISI 304 stainless steel powder. Powder particles with an average size of 35 \(\upmu\)m or less were used for the SLM experiments. The chemical composition of the powder is shown in Table 1. The parts were built on a copper base plate. The high thermal conductivity of copper allows heat to pass through quickly, and prevents the adhesion of the laser-melted thin layer during the SLM process. Hence, thin laser-melted parts fabricated on a copper plate can be easily detached without the application of any post-separation process. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Element** & **Fe** & **Cr** & **Ni** & **Mo** & **Mn** & **Si** \\ \hline wt. \% & Bal. & 18.00 & 9.00 & 2.25 & 1.00 & 0.20 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Chemical composition of AISI 304 stainless steel powder (wt.%). Figure 2: Scanning electron microscope (SEM) micrographs of spherical AISI 304 stainless steel powder. A fiber laser (IPG YLR-200, IPG Photonics Company, Burbach, Germany) irradiation system with a maximum power of 200 W is used. The wavelength of the laser is 1.07 \(\upmu\)m, and the laser beam diameter is 0.08 mm at the focal position. A scanner (hurrySCAN(r)20, SCANLAB, Puchheim, Germany) is used to control the laser scanning. The vertical movement of the cylinder is driven by a motor. Table 2 shows the laser process parameters used in the SLM experiments. Figure 3 schematically shows the single-track SLM process. In a single-track SLM process with a copper base plate, the powder layering thickness is critical in obtaining a sound bead. As shown in Figure 3a, a sufficient sized melted bead is not obtained when the powder layering thickness is 0.2 mm or less. At a low powder-layering thickness, a large amount of heat of the irradiated laser beam is rapidly dissipated from the copper plate and, therefore, a complete melting of the powder becomes hard to achieve at a low powder layering thickness. In contrast, a fully melted bead is obtained when the powder layering thickness is approximately 0.5 mm, as shown in Figure 3b. In this case, an irradiated laser beam with a large amount of heat is used for melting the powder, and the amount of heat loss from the copper plate is relatively small. Owing to the steady melting of the powder and the uniform solidification of the molten pool on the copper base, a sound thin-layered bead with 0.4 mm width has been obtained at this layering thickness. Figure 3c shows a layering thickness of above 0.6 mm, the shape of the bead becomes irregular owing to the free consolidation without the controlled solidification effect of a copper plate. Therefore, single-track SLM experiments were conducted using a laser power of 200 W, a scan rate of 110 mm/s, and a powder layering thickness of 0.5 mm. \begin{table}
\begin{tabular}{c c} \hline Laser Power (W) & 200 \\ Scan rate (mm/s) & 110 \\ Fill-spacing (mm) & 0.06 \\ Powder layering thickness (mm) & 0.2–0.6 \\ Fabricated shape type & square, circle, rectangle \\ \hline \end{tabular}
\end{table} 
Table 2: Process parameters used in selective laser melting (SLM). Figure 3: Single-track beads fabricated at powder layering thickness of (**a**) 0.2 and (**b**) 0.5 mm (**c**) 0.6 mm. Figure 4 shows a schematic of the multi-track SLM process. Figure 5 shows cross-sectional views of beads obtained under various laser heat input conditions. At a laser power of 100 W, an unstable irregular bead is obtained owing to insufficient heat input and heat dissipation through the copper plate, as shown in Figure 5a,b shows a bead obtained at a laser power of 150 W. An unstable irregular bead still occurs owing to insufficient heat input and heat dissipation through the copper plate. A sound fully melted bead is obtained at a laser power of 200 W, as shown in Figure 5c. In this case, an irradiated laser beam with a large amount of heat is used for melting the powder, and a uniform solidification of the molten pool on the copper base steadily occurs.