A 316L stainless steel [SS316L] plate was fabricated without pores by selective laser melting (SLM) in a vacuum. SS316L has excellent properties such as high corrosion resistance and hardness, but forming complicated structures is challenging due to difficulties working the material. SLM forms a 3D material by building it layer by layer. In SLM process, a denudation zone is caused to form near the laser scan path while laser irradiation. The denudation zone caused to form a layer having an un-uniform thickness and also leads to a decrease accuracy of fabrication. There are many unknown controlling factors about the basis of denudation zone generation. In this study, in order to clarify the mechanism of the denudation zone formation process, SS316L is fabricated by SLM in a vacuum and the width of denudation zone is measured by microscope. The ambient pressure is varied from 10 Pa to 10 ⁵ Pa using a vacuum pump, and argon gas. As the results, at the ambient pressure of 10⁵ Pa, the width of denudation zone is 0.81 mm, and the width of denudation zone at 300 Pa was improved to 0.27 mm. It is clarified that the width of denudation decreases with the decrease of the ambient pressure.
Stainless-steel type 316L (SS316L) plate was fabricated by selectively laser melting method (SLM) in vacuum. SS316L has excellent properties such as a high corrosion resistance and hardness, but fabricating complicated structures is challenging due to difficulties in processing the material. Although SLM can fabricate complicated shapes because it builds a 3D material layer-by-layer from a powder, some issues have yet to be resolved. One is that spatter is generated by metal powder scattering during laser irradiation. Another one is the denudation zone due to the balling effect. Spatter is considered to be dominated by the recoil pressure of fume caused by melting and evaporation of metal, and it is not possible to suppress the expansion of fume and reduce spattering by changing the atmospheric pressure. In addition, it is considered that the balling effect is dominated by the surface tension of the molten land under atmospheric pressure with a lot of convection. Therefore, in this study, SS316L plate was fabricated by changing the atmospheric pressure in the chamber, and the effect of atmospheric pressure on the spattering and balling effects was clarified. First, SS316L powder was set in a vacuum chamber, depressurized using a vacuum pump, and then irradiated with a single-mode fiber laser. Spatter was captured using a high-speed video camera during laser irradiation of SS316L powder. After that, polishing, edging, and cross-section observation were performed. As a result, it was found that when the atmospheric pressure was lowered, the spatter amount and bead the height decreased, and the denudation zone increased.
A pure titanium (Ti) plate was fabricated by selective laser melting (SLM) in a vacuum. Ti is attractive materials for medical, aerospace, and automotive applications, because they have properties of biocompatibility, high corrosion and erosion resistance, and mechanical resistance, but forming complicated structures is challenging due to difficulties working the material. Although some studies have reported to form pores in SLMed samples due to spattering generated by laser irradiation, and there are few reports that investigate the details of the correlation between spatter and pores. Spatter results in an insufficient input energy to the powder bed because the laser is absorbed by the spatter particles. Consequently, technology to suppress the amount of spatter for SLM processes is needed. In this study, the quantitatively evaluation method for the amount of spatter was developed with high speed video camera while the SLM processes.
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