Challenges in Three-Dimensional Printing of High-Conductivity Copper

Abstract

With recent advancements in additive manufacturing (AM) technology, it is possible to deposit copper conductive paths and insulation layers of an electric machine in a selective controlled manner. AM of copper enables higher fill factors that improves the internal thermal conduction in the stator core of the electric machine (induction motor), which will enhance its efficiency and power density. This will reduce the motor size and weight and make it more suitable for aerospace and electric vehicle applications, while reducing/eliminating the rare-earth dependency. The objective of this paper is to present the challenges associated with AM of copper coils having 1 × 1 mm cross section and complex features that are used in producing ultra-high efficiency induction motor for traction applications. The paper also proposes different approaches that were used by the authors in attempts to overcome those challenges. The results of the developed technologies illustrate the important of copper powder treatment to help in flowing the powder easier during deposition. In addition, the treated powder has higher resistance to surface oxidation, which led to a high reduction in porosity formation and improved the quality of the copper deposits. The laser powder direct energy deposition (LPDED) process modeling approach helps in optimizing the powder deposition path, the laser power, and feed rate that allow the production of porosity free thin wall and thin floor components. The laser powder bed fusion (LPBF) models identify the optimum process parameters that are used to produce test specimens with >90% density and minimum porosity.

Characteristics and Processing of Hydrogen-Treated Copper Powders for EB-PBF Additive Manufacturing

“…However, the poor absorptivity, lower ambient temperatures, and lack of a vacuum atmosphere may contribute to a significantly different outcome. In the work by El-Wardany et al [6], a relatively high oxygen copper powder was heat treated in a forming gas environment in order to remove the surface oxides and subsequently be coated with a polydimethylsiloxane (PDMS) polymer. No further data on the chemistry, properties, or microstructure of this material were reported, other than the observation of the formation of unexpectedly large pores in single track welds that were not present in the untreated powders.…”

“…Hydrogen, carbon monoxide, and ethanol are commonly employed reducing agents of Cu 2 O and CuO in thin films [31][32][33]. El-Wardany et al [6] treated copper powders for L-PBF in a heated forming gas atmosphere (4% H 2 + Ar bal. ), theorizing that the hydrogen would reduce the surface Cu 2 O films into Cu + H 2 O, however, no quantitative data on the composition of the powders or solid samples produced were provided [6].…”

“…El-Wardany et al [6] treated copper powders for L-PBF in a heated forming gas atmosphere (4% H 2 + Ar bal. ), theorizing that the hydrogen would reduce the surface Cu 2 O films into Cu + H 2 O, however, no quantitative data on the composition of the powders or solid samples produced were provided [6]. In addition, this study only considered the reduction of oxides from the surface of the Cu powders, and did not address the possibility that hydrogen also reduces the internal oxides.…”

3D Printing of Highly Pure Copper

“…However, 3D printing of pure copper has several significant processing challenges that need to be addressed. Due to copper's high thermal conductivity, the melt area experiences rapid heat dissipation and high local thermal gradients, resulting in delamination, layer curling, and part failure [40,41]. Furthermore, the post-build powder removal and recovery of the printed parts might be impeded by the high ductility of copper while the tendency of powder agglomeration could lower overall flowability and hinder powder deposition.…”

Additive manufacturing of CuCr1Zr by development of a gas atomization and laser powder bed fusion routine

“…However, defects in LPBF-built parts lead to a deterioration of the mechanical properties. In [27], parameter studies on oxygen-free, high-conductivity (OFHC) copper with small amount of phosphor (0.03-0.6 wt.%) were performed and samples reached relative densities of only 92% for laser sources of 300 W (1060 nm). For Cu-Cr-Zr-Ti alloys, a density of 97.9% was obtained [28], when using a laser source of 400 W. However, the porosity led to a reduction of the ultimate tensile strength of 20 to 25% compared to hot-rolled samples, which might be caused by residual porosity in the LPBF material [28].…”