High-precision laser powder bed fusion processing of pure copper

Abstract

Pure copper is widely used in the industry as the base metal for heat transfer and electromagnetic applications, thanks to its superior electrical and thermal conductivity. Complex pure copper components have been attempted by various additive manufacture (AM) techniques. Among them, laser powder bed fusion (LPBF) is competent to print smooth curved surfaces and complex geometries due to its high resolution and powder bed support. However, the fabrication of pure copper by LPBF generally requires a laser power of more than 400 W (usually up to 1000 W) due to the high infrared laser reflection and thermal conductivity of pure copper. Therefore, the laser optics could be damaged by the back reflection of high-power laser. The LPBF with a short-wavelength laser has also been attempted but with a low resolution of 500 µm at present. In this work, a high-precision LPBF (hp-LPBF) system with small laser spot (25 µm), fine powder (5–25 µm), and small layer thickness (10 µm) is developed, which can achieve the full densification of pure copper components with high resolution and low roughness at a relatively low laser power. The thin walls and cube bulks were employed to investigate the effect of parameters on the resolution, roughness, and performance. As a result, the as-built pure copper components with the relative density (RD) (99.6%) and the electrical conductivity of 76.1% International Annealed Copper Standard (IACS) are fabricated by the optimal parameters of the laser power of 200 W, the scan speed of 600 mm/s, the hatch distance (HD) of 0.05 mm. After heat treatment, the electrical performance can be further increased to 96% IACS. The pure copper parts with complex cellular structures were printed with 100 µm wall thickness and the top/side/bottom surface roughness Ra of 3.3/14.8/19.2 µm. Overall, the hp-LPBF has demonstrated its capability to print finer and smoother pure copper parts with the same level of relative density and properties compared to conventional LPBF.