Laser metal deposition of copper on diverse metals using green laser sources

Abstract

Green laser sources are advantageous in the processing of copper due to the increase of absorptivity compared with more commonly available infrared lasers. Laser metal deposition of copper with a green laser onto various substrate metals namely copper, aluminium, steel and titanium alloy was carried out and observed through high-speed imaging. The effects of process parameters such as laser power, cladding speed and powder feed rate, and material attributes such as absorptivity, surface conditions and thermal conductivity are tied together to explain the size and geometry of the melt pool as well as the fraction of the power used for melting material. The copper substrate has the smallest melt pool with a high angle, followed by aluminium, steel and titanium alloy. The incorporation times for powder grains in the melt pools vary based on the substrate materials. Its dependency on material properties, including surface tension forces, melting temperatures and material density, is discussed. Oxide skins present on melt pools can affect powder incorporation, most significantly on the aluminium substrate. The lower limits of the fraction of power irradiated on the surface used purely for melting were calculated to be 0.73%, 2.94%, 5.95% and 9.78% for the copper, aluminium, steel and titanium alloy substrates, respectively, showing a strong dependence on thermal conductivity of the substrate material. For a copper wall built, the fraction was 2.66%, much higher than a single clad on a copper substrate, due to reduced workpiece heating. The results of this paper can be transferred to other metals with low absorptivity such as gold.

Highly conductive and strong CuSn0.3 alloy processed via laser powder bed fusion starting from a tin-coated copper powder

“…Changing the laser wavelength from the infrared region (fiber laser λ = 1070 ± 10 nm) to the visible region (green laser λ = 515 nm [14], and blue laser λ = 450 nm [15]) is inspired by the low optical reflectivity of copper for the visible radiation. Although fully dense copper parts could be manufactured using green or blue lasers via other laser-based AM processes [16][17][18], researchers have not yet disclosed the density, mechanical, electrical, or thermal properties of such LPBF fabricated parts. Moreover, the newly developed green or blue laser technology is costly and still in the research phase.…”

Surface Modified Copper Alloy Powder for Reliable Laser-based Additive Manufacturing

“…Therefore, the authors discourage the use of high-power fiber laser for processing such a highly reflective material powder and suggest to use green or blue lasers, for which copper exhibits higher optical absorptivity due to the interband electronic transition mechanism [15]. Recently, green [16,17] and blue [18] lasers have been used in laser metal deposition (LMD) [19,20], and laser welding [21] processes and attempts are being made to process pure copper via LPBF. However, neither mechanical nor electrical or thermal properties of such parts have yet been reported.…”

Laser Powder Bed Fusion of Metal Coated Copper Powders

“…This technology has attracted much attention in the scientific community for the possibility to manufacture part geometries impossible to manufacture using conventional processing methods [3]. It is also possible to produce materials with spatially varying microstructures, or including metastable phases [4,5]. L-PBF has become an industrially relevant method for manufacturing small batches or individualized parts quickly [6].…”

“…The manufacturing of dense, defect-free parts is, however, challenging due to the high thermal conductivity (400 W/mK) and high optical reflectivity ( R ), the complement of absorptivity ( A ) , in the near infrared spectra (>99%) of copper. This means that most of the energy put into the system is either reflected or quickly dissipated away [ 5 ].…”

“…Commercial machines using green laser sources have been advertised [16], but scientific literature is scarce on the topic. Direct metal deposition (DMD), an AM technique similar to L-PBF, as well as laser welding of copper with a green laser source have been reported in the scientific literature [5,17,18]. Green lasers have also been used in combination with infrared lasers in laser welding processes [19,20] where the green laser helped stabilizing the process.…”