Additive Manufacturing is becoming increasingly&nbsp; 
important due to its possibilities. Processes such as selective&nbsp; 
laser melting, electron beam melting or binder jetting are used&nbsp; 
to manufacture industrial metal parts. The starting material for&nbsp; 
these techniques is metal powder with a particle size of approx.&nbsp; 
30 to 100 microns, depending on the process. &nbsp; 
Common processes for powder production are e.g. gas or&nbsp; 
water atomization. Disadvantages of these techniques are the&nbsp; 
non-spherical particles and the wide size distribution. Today's&nbsp; 
Additive Manufacturing technologies require a high-quality,&nbsp; 
spherical powder with a narrow particle size distribution. After&nbsp; 
powder production, sieving or similar separation methods are&nbsp; 
required to sort the particles by size and achieve the desired size&nbsp; 
distribution. Particles that don’t have the desired size, have to be&nbsp; 
discarded. The high consumption of inert gas (argon) for gas&nbsp; 
atomization and the complex screening process result in high&nbsp; 
costs for the powder produced.&nbsp; 
One alternative method for producing monodisperse and&nbsp; 
spherical particles from molten metal is droplet formation using&nbsp; 
Plateau-Rayleigh instability. This effect causes a liquid jet to&nbsp; 
break up into droplets of the same size. This breakup can be&nbsp; 
stimulated by modulating the jet velocity at a specific frequency.&nbsp; 
In free fall, the droplet shape becomes spherical due to the&nbsp; 
surface tension of the melt. In this way a monodisperse powder&nbsp; 
with spherical particles can be produced. The size of the&nbsp; 
generated particles depends on the modulation wavelength,&nbsp; 
while the instability has its greatest effect on a specific&nbsp;wavelength proportional to the jet diameter. By varying the&nbsp; 
modulation frequency during the process, precisely defined&nbsp; 
fractions of certain particle sizes can be generated. In this way,&nbsp; 
powders with tailor-made particle size distribution can be&nbsp; 
produced for specific applications.&nbsp; 
In this work a droplet generator for molten solder (Sn 37%,&nbsp; 
Pb 63%) was designed, built and tested. Due to its temperature&nbsp; 
stability and mechanical properties, the body of the droplet&nbsp; 
generator was manufactured from the polymer PEEK (polyether&nbsp; 
ether ketone). The modulation was performed with a piezo stack&nbsp; 
actuator controlled by a waveform generator and an amplifier. A&nbsp; 
sapphire nozzle with a diameter of &nbsp;200 microns was used for jet&nbsp; 
forming.&nbsp; 
The droplet size, jet velocity and modulation frequencies&nbsp; 
were characterized and compared with theoretical calculations.&nbsp; 
Jet breakup and drop formation were investigated with a high- 
speed video camera. The generated particles were examined for&nbsp; 
size and shape by scanning electron microscopy. As a result, this&nbsp; 
work shows the potential of using this method to produce high&nbsp; 
quality powder for metal-based Additive Manufacturing&nbsp; 
technologies. Further work can be carried out to process metals&nbsp; 
with higher melting temperatures and to increase the throughput&nbsp; 
of the system.

Production of Spherical Monodisperse Metal Powders by Means of the Plateau-Rayleigh Instability of a Liquid Metal Jet

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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