Effect of Particle Size Distribution on Laser Powder Bed Fusion Manufacturability of Copper

Massimiliano Bonesso,Adriano Pepato,Simone Mancin,Razvan Dima,Pietro Rebesan,Claudio Gennari,Irene Calliari

doi:10.1007/s00501-021-01107-0

Abstract

One of the major benefits of the Laser Powder Bed Fusion (LPBF) technology is the possibility of fabrication of complex geometries and features in only one-step of production. In the case of heat exchangers in particular, this is very convenient for the fabrication of conformal cooling channels which can improve the performance of the heat transfer capability. Yet, obtaining dense copper parts printed via LPBF presents two major problems: the high reflectivity of 1 μm (the wavelength of commonly used laser sources) and the high thermal conductivity of copper that limits the maximum local temperature that can be attained. This leads to the formation of porous parts.In this contribution, the influence of the particle size distribution of the powder on the physical and mechanical properties of parts produced via LPBF is studied. Three copper powders lots with different particle size distributions are used in this study. The effect on densification from two laser scan parameters (scan speed and hatching distance) and the influence of contours scans on the lateral surface roughness is reported. Subsequently, samples manufactured with the optimal process parameters are tested for thermal and mechanical properties evaluation.

Highlights

ISO/ASTM 52900 defines the Powder Bed Fusion (PBF) as the additive manufacturing process in which thermal energy selectively fuses regions of a powder bed [1]
Broad particle size distribution (PSD) leads to a higher powder bed density that favours the densification process [15], and enhances the thermal conductivity of the powder [16], which is a drawback in the case of pure copper
The sample manufactured using Powder C showed a thermal conductivity of 227.8 W/mK, in this case the reduction of the conductivity could be due to the chemical composition of the starting powder and to the presence of porosities and un-melted particles. This contribution investigates the fabrication by Laser Powder Bed Fusion (LPBF) of copper parts using powders with different particle size distribution

Summary

Introduction

ISO/ASTM 52900 defines the Powder Bed Fusion (PBF) as the additive manufacturing process in which thermal energy selectively fuses regions of a powder bed [1]. In order to overcome this issue, different approaches have been studied: high density parts (>98%) were manufactured using higher laser power (up to 1000 W) [6, 8] and the use of a green laser (515 nm) for which copper has lower reflectivity is investigated by Fraunhofer for Laser Technology ILT [9]. These approaches for printing pure copper, are not suitable for commercially available LPBF machines, which have a low laser power (400 W Max) and laser wavelength of around 1080 nm. The feasibility of the SLM production of dense pure copper parts at low laser power (max 200 W) was demonstrated utilizing a finer distribution of powders [12]

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Results

Conclusion