Development of powder bed fusion of pure copper with a 440 nm blue laser using wavelength beam combining of direct diode laser
摘要
A short-wavelength laser with a high power output and small spot size is required to improve the quality and efficiency of powder bed fusion (PBF) for pure copper parts. We employed a PBF with laser beam/metal (PBF-LB/M) system using a wavelength beam combining method to achieve a 440 nm blue laser with a maximum laser power of 400 W and spot size of 100 μm. We investigated the influence of laser power and scanning speed on the morphological changes of single tracks and evaluated the surface waviness of single layers fabricated at various overlap ratios. Based on these findings, a range of building conditions that reduce the porosity of the built parts was established. The results showed that the proposed PBF-LB/M system could produce copper parts on a pure copper substrate without preheating. A uniform geometry of a single track was obtained at a laser power of 300–350 W and scanning speed of 100–250 mm/s. For a single layer structure, the arithmetic mean height Pa of the built surface exhibited its highest value of 11 μm at an overlap ratio of 0.1, and decreased to 8.1 μm at an overlap ratio of 0.5. A relative density of 99.75% of the built structure was achieved at a volumetric energy density (VED) of 270 J/mm3. The porosity of the built structure decreased with an increase in the flow rate of the N2 inert gas in the building chamber, and its value changed from 0.95% to 0.25% at a flow rate of 10–100 L/min. The high blue laser absorptivity of pure copper can reduce the VED by more than 50% compared with that of the infrared laser to obtain fully dense parts.