A novel convergent–divergent annular nozzle design for close-coupled atomisation

Abstract

Additive manufacturing processes such as selective laser melting and electron beam melting require small particle sizes. A widely used technique to produce suitable powders is closecoupled atomisation. To further decrease the achieved particle sizes, the annular geometry of the gas nozzle is changed to a convergent-divergent (CD) profile. This novel configuration is capable of operating stably at low pressures of 0.8 MPa and above. Beyond that, the unwanted effects of lick-back are avoided. Different nozzles with conventional and convergent-divergent annular geometry have been designed based on fluid-flow calculations. The aspiration pressure was measured to determine stable process windows. Powders from a CuSn alloy were produced using cold and hot gas atomisation to show the influence on the process stability, particle size and morphology. High-speed recordings are used to investigate the process conditions of the different nozzle configurations.

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

“…During the process, the close-coupled mode was used where the gas flow was regulated and fed in a way that a low-pressure was established underneath the nozzle (see blue arrows in Fig. 2a) resulting in the formation of particles sizes below 100 μm [23,24]. Figure 2b shows the melt flow and the visible formation of the low-pressure area underneath the nozzle.…”

“…Impurities and gas inclusions being already present in the powder are incorporated during the melting process and lead to pores and imperfections. One possibility to produce LPBF powders with suitable particle size distributions in the range between 10 μm and 100 μm is gas atomization by application of the close-coupled method [23,24].…”

Adjustment of Mechanical Properties of Medium Manganese Steel Produced by Laser Powder Bed Fusion with a Subsequent Heat Treatment

“…Pure iron, manganese, silicon and aluminum were melted in an Al 2 O 3 crucible under a protective argon atmosphere to a melt temperature of 1715 °C (corresponds to about 200 °C above liquidus temperature). After a homogenization time of 15 min, the melt was atomized in a Close-Coupled-Atomizer (INDUTHERM Erwärmungsanlagen GmbH, Walzbachtal, Germany) equipped with a convergent-divergent gas nozzle [ 41 ]. The process parameters used for the atomization are summarized in Table 1 .…”

Austenitic Stainless Steel Powders with Increased Nitrogen Content for Laser Additive Manufacturing

“…The most common process to produce metal powder for laser additive manufacturing is gas atomization: a molten metal stream is atomized by high pressure gas jets into small metal droplets, forming metal particles after rapid solidification. In this study, the gas atomization of the austenitic stainless steels was carried out on a self-constructed powder plant (PA7 at the University of Bremen) with a melting capacity of 0.7 L [26][27][28]. The main process parameters, that are selected based on our previous gas atomization experiments of steels, are listed in Table 2.…”

“…The process gas was converted from evaporated liquid nitrogen or evaporated liquid argon with a high purity of 99.99%. The steel melt flowed through a delivery tube (2.5 mm diameter) at the bottom of the crucible and was atomized by means of a self-developed close-coupled atomizer (GD26) [26]. The atomization gas pressure was 1.6 MPa, corresponding to a gas mass flow rate of 590 kg/h for nitrogen and 775 kg/h for argon.…”