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.
Highlights
Additive manufacturing is a technology through which components are manufactured by adding material in layers
Copper tracks were successfully cladded onto the four substrate materials: copper, aluminium, steel and titanium alloy
Steel and titanium alloy substrates follow the order of decreasing laser power requirement for the same cladding speed
Summary
Additive manufacturing is a technology through which components are manufactured by adding material in layers. Pogson et al [17] mention that copper structures of increasing importance such as micro-heat exchangers are difficult to manufacture through conventional methods. Int J Adv Manuf Technol (2020) 107:1559–1568 copper an interesting material for tooling inserts and cooling components as well as in electrical components when it is precipitation strengthened or alloyed. Deposition of a functionally gradient material with varying fractions of copper and nickel through LMD has been carried out with a CO2 laser by Mazumder and Stiles [16]. Imran et al [12] succeeded at depositing tool steel powder onto a copper substrate through LMD, with and without a buffer layer, intended to make bimetallic tooling using a CO2 laser
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